Black screen after login

edit

Hey guys, I tried logging in this morning and was welcomed with a black screen (cursor still showed). I swapped over to another tty and noticed that kwin was stuck running at 100%, but when I tried to replace it it complained about a fatal error. Things were working fine last night, but here's some changes that happened recently:

• updated akmod-nvidia
• noticed Fedora (4.0.4-202.fc21.x86_64) 21 added to the grub list

So far I can login by booting into the old Fedora (3.19.5-200.fc21.x86_64) 21, and choosing KDE Plasma Failsafe login. I tried downgrading akmod-nvidia to 346.72-1, but the problem still persisted.

Any ideas? Thank you