I try to play on forge with mods it loads and doesnt start up the client Im on windows 7 if it helps
[09:22:17] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[09:22:18] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[09:22:18] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[09:22:18] [main/INFO] [FML]: Forge Mod Loader version 7.10.25.1208 for Minecraft 1.7.10 loading
[09:22:18] [main/INFO] [FML]: Java is Java HotSpot Client VM, version 1.8.0_31, running on Windows 7:x86:6.1, installed at C:\Program Files (x86)\Java\jre1.8.0_31
[09:22:18] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[09:22:18] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
[09:22:18] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[09:22:18] [main/ERROR] [LaunchWrapper]: Unable to launch
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_31]
at java.util.ArrayList$Itr.remove(Unknown Source) ~[?:1.8.0_31]
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:?]
Java HotSpot Client VM warning: Using incremental CMS is deprecated and will likely be removed in a future release