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Minecraft and Forge worked perfectly fine a few days ago. Then I had to factory default my computer, so everything was wiped. I downloaded Minecraft, Forge, and Java as per usual. Vanilla Minecraft works perfectly fine. I launch it with Forge, it acts like it's loading then just disappears. Not even in my task manager. I had read a few places to try downgrading Java. So I did, first to 8u11, now to 7 and still nothing. So I purged my computer of all things Minecraft, Forge, and Java to start over. Still nothing. So I'm at a loss at what to do. I always only use the automated install for Forge and I've never used any other launchers besides the original. I did manage to get what I think is an error/crash report.

[code][spoiler][code] [21:21:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker [21:21:11] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker [21:21:11] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker [21:21:11] [main/INFO] [FML]: Forge Mod Loader version 7.2.217.1147 for Minecraft 1.7.2 loading [21:21:11] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_25, running on Windows 7:amd64:6.1, installed at C:\Program Files (x86)\Minecraft\runtime\jre-x64\1.8.0_25 [21:21:11] [main/INFO] [FML]: Loading tweaker optifine.OptiFineForgeTweaker from OptiFine_1.8.1_HD_U_B4.jar [21:21:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker [21:21:11] [main/INFO] [LaunchWrapper]: Loading tweak class name optifine.OptiFineForgeTweaker [21:21:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker [21:21:11] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker [21:21:11] [main/ERROR] [LaunchWrapper]: Unable to launch java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_25] at java.util.ArrayList$Itr.remove(ArrayList.java:865) ~[?:1.8.0_25] 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(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release [/code][/spoiler]
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Wow! I am having the exact same issue! My miecraft was working with forge...now it just disappears after I click play. I did everything you did. Even tried rolling back my graphics drivers. As far as I can tell, it seems that the graphics drivers are usually an issue when it comes to forge. I will let you know if I find anything.

DUDE! I got it working!!!! Here is the link to the website for the fix:

http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2206446-forge-1-6-4-1-7-2-java-8-compatibility-patch



Make sure to follow the instructions carefully! The last paragraph of the section labeled Vanilla is the important stuff. Hope this help!!!

As far as the Optifine thing, I thought I had taken it out to install Forge as I know they don't work well together.

I followed the link Ranger1333 posted, followed the instructions to the T and it still didn't work. Here's what i got this time.