When I click play at the bottom usually it downloads then lets me get into the main menu. For 1.8 it downloads about 95% of the files, then stops when it's downloading the .jar .
I get this error message when it stops trying to download:
Error: Could not find or load main class net.minecraft.client.main.Main
Java HotSpot(TM) Client VM warning: Using incremental CMS is deprecated and will likely be removed in a future release
I think it's probably a problem with Java 8 but I just wanted to be sure this is reported, because I couldn't find anything similar in my search.
No Java 8 is running fine with Minecraft. The warning is just about some deprecated options.
Please attach the complete output of the "Launcher Log" which can be found on the second tab of the launcher.