This is what java tells me:

[02:18:19] [main/INFO] [GradleStart]: No arguments specified, assuming client.

[02:18:19] [main/INFO] [GradleStart]: Extra: []

[02:18:19] [main/INFO] [GradleStart]: Running with arguments: [--userProperties, {}, --assetsDir, C:/Users/seth/.gradle/caches/minecraft/assets, --assetIndex, 1.7.10, --accessToken, {REDACTED}, --version, 1.7.10, --tweakClass, cpw.mods.fml.common.launcher.FMLTweaker, --username, ForgeDevName]

[02:18:19] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker

[02:18:19] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker

[02:18:19] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker

[02:18:19] [main/INFO] [FML]: Forge Mod Loader version 7.10.18.1180 for Minecraft 1.7.10 loading

[02:18:20] [main/INFO] [FML]: Java is Java HotSpot 64-Bit Server VM, version 1.8.0_20, running on Windows 8.1:amd64:6.3, installed at C:\Program Files\Java\jre1.8.0_20

[02:18:20] [main/INFO] [FML]: Managed to load a deobfuscated Minecraft name- we are in a deobfuscated environment. Skipping runtime deobfuscation

[02:18:20] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[02:18:20] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker

[02:18:20] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker

[02:18:20] [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:?]

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_20]

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_20]

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_20]

at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_20]

at GradleStart.bounce(GradleStart.java:107) [start/:?]

at GradleStart.startClient(GradleStart.java:100) [start/:?]

at GradleStart.main(GradleStart.java:55) [start/:?]

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0

at GradleStart.main(GradleStart.java:59)

Java HotSpot 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release

Read the EAQ.

I ran into a problem with Java 1.8_20 not being able to do Minecraft.. I recommend uninstalling 1.8 of Java and making sure to reinstall 1.7_65 (or whatever).. I still had a lingering Java.exe somehow, after uninstalling .. and had to reinstall the 1.7 stuffs..