Well, i install forge (any version) i click the Play button and Minecraft does not start, i check at the processes of Windows and the only Minecraft's process is the one from the launcher, after some seconds that process disappears and Minecraft is still not Launching, it's curious because before that (like 9 or 10 hours) it were working perfectly

Help :C

We can't help without the logs.

 

"It doesn't work" or "it's broken" doesn't help us.

not sure how to do spoiler, my apologies, but same problem as above, I hope this is what you need

 

[02:23:33] [main/INFO] [FML/]: Forge Mod Loader version 7.10.25.1208 for Minecraft 1.7.10 loading

[02:23:33] [main/INFO] [FML/]: Java is Java HotSpot Client VM, version 1.8.0_20, running on Windows 8.1:x86:6.3, installed at C:\Program Files (x86)\Java\jre1.8.0_20

[02:23:33] [main/DEBUG] [FML/]: Java classpath at launch is C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\minecraftforge\forge\1.7.10-10.13.0.1208\forge-1.7.10-10.13.0.1208.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\minecraft\launchwrapper\1.9\launchwrapper-1.9.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\ow2\asm\asm-all\4.1\asm-all-4.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\typesafe\akka\akka-actor_2.11\2.3.3\akka-actor_2.11-2.3.3.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\typesafe\config\1.2.1\config-1.2.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-actors-migration_2.11\1.1.0\scala-actors-migration_2.11-1.1.0.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-compiler\2.11.1\scala-compiler-2.11.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\plugins\scala-continuations-library_2.11\1.0.2\scala-continuations-library_2.11-1.0.2.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\plugins\scala-continuations-plugin_2.11.1\1.0.2\scala-continuations-plugin_2.11.1-1.0.2.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-library\2.11.1\scala-library-2.11.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-parser-combinators_2.11\1.0.1\scala-parser-combinators_2.11-1.0.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-reflect\2.11.1\scala-reflect-2.11.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-swing_2.11\1.0.1\scala-swing_2.11-1.0.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-xml_2.11\1.0.2\scala-xml_2.11-1.0.2.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\sf\jopt-simple\jopt-simple\4.5\jopt-simple-4.5.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\lzma\lzma\0.0.1\lzma-0.0.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\mojang\realms\1.3.1\realms-1.3.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\commons\commons-compress\1.8.1\commons-compress-1.8.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\httpcomponents\httpclient\4.3.3\httpclient-4.3.3.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\commons-logging\commons-logging\1.1.3\commons-logging-1.1.3.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\httpcomponents\httpcore\4.3.2\httpcore-4.3.2.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\java3d\vecmath\1.3.1\vecmath-1.3.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\sf\trove4j\trove4j\3.0.3\trove4j-3.0.3.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\ibm\icu\icu4j-core-mojang\51.2\icu4j-core-mojang-51.2.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\paulscode\codecjorbis\20101023\codecjorbis-20101023.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\paulscode\codecwav\20101023\codecwav-20101023.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\paulscode\libraryjavasound\20101123\libraryjavasound-20101123.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\paulscode\librarylwjglopenal\20100824\librarylwjglopenal-20100824.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\paulscode\soundsystem\20120107\soundsystem-20120107.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\io\netty\netty-all\4.0.10.Final\netty-all-4.0.10.Final.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\google\guava\guava\16.0\guava-16.0.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\commons\commons-lang3\3.2.1\commons-lang3-3.2.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\commons-codec\commons-codec\1.9\commons-codec-1.9.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\java\jinput\jinput\2.0.5\jinput-2.0.5.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\net\java\jutils\jutils\1.0.0\jutils-1.0.0.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\google\code\gson\gson\2.2.4\gson-2.2.4.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\com\mojang\authlib\1.5.16\authlib-1.5.16.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\logging\log4j\log4j-api\2.0-beta9\log4j-api-2.0-beta9.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\apache\logging\log4j\log4j-core\2.0-beta9\log4j-core-2.0-beta9.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl\2.9.1\lwjgl-2.9.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl_util\2.9.1\lwjgl_util-2.9.1.jar;C:\Users\Michael\AppData\Roaming\.minecraft\libraries\tv\twitch\twitch\5.16\twitch-5.16.jar;C:\Users\Michael\AppData\Roaming\.minecraft\versions\1.7.10-Forge10.13.0.1208\1.7.10-Forge10.13.0.1208.jar

[02:23:33] [main/DEBUG] [FML/]: Java library path at launch is C:\Users\Michael\AppData\Roaming\.minecraft\versions\1.7.10-Forge10.13.0.1208\1.7.10-Forge10.13.0.1208-natives-369587799531814

[02:23:33] [main/DEBUG] [FML/]: Enabling runtime deobfuscation

[02:23:33] [main/DEBUG] [FML/]: Instantiating coremod class FMLCorePlugin

[02:23:33] [main/DEBUG] [FML/]: Added access transformer class cpw.mods.fml.common.asm.transformers.AccessTransformer to enqueued access transformers

[02:23:33] [main/DEBUG] [FML/]: Enqueued coremod FMLCorePlugin

[02:23:33] [main/DEBUG] [FML/]: Instantiating coremod class FMLForgePlugin

[02:23:33] [main/DEBUG] [FML/]: Added access transformer class net.minecraftforge.transformers.ForgeAccessTransformer to enqueued access transformers

[02:23:33] [main/DEBUG] [FML/]: Enqueued coremod FMLForgePlugin

[02:23:33] [main/DEBUG] [FML/]: All fundamental core mods are successfully located

[02:23:33] [main/DEBUG] [FML/]: Discovering coremods

[02:23:33] [main/INFO] [LaunchWrapper/]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[02:23:33] [main/INFO] [LaunchWrapper/]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker

[02:23:33] [main/INFO] [LaunchWrapper/]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[02:23:33] [main/ERROR] [LaunchWrapper/]: Unable to launch

java.util.ConcurrentModificationException

at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_20]

at java.util.ArrayList$Itr.remove(Unknown Source) ~[?:1.8.0_20]

at net.minecraft.launchwrapper.Launch.launch(Launch.java:117) [launchwrapper-1.9.jar:?]

at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.9.jar:?]

 

Read the EAQ.

Nope, it's not an error, it just doesn't start, and it doesn't have logs too, i just make a new .minecraft folder, install forge, start minecraft (with the forge version) and the game does not launch

Are you saying that the logs folder is completely empty? 

I think so, i'm gonna check it out... This is the only "log" that i have: http://gyazo.com/2265add703100277d861bd2307d2819e

Actually, it is not in a "logs" folder, that folder doesn't exists in my .minecraft

Your issue is "Java is Java HotSpot Client VM, version 1.8.0_20" java 1.8.0_20 causes "java.util.ConcurrentModificationException" with forge.  Downgrade to Java 1.8.0_11 if you need Java 8, or Java 7 otherwise.

In simples words, what i gotta do?

I say this because i'm from Spain and i didn't understood very well what you told me, i gotta download an older Java 8 version?

I have to uninstall something? I don't know what i gotta do, .

Can you tell me please?

Thanks everyone who helped me, it worked

I have a Minecraft YouTube serie and i weren't capable to make it without forge, thanks