App Store won't let me log in
I'm using Lion and I can't update to Mountain Lion because the app store won't let me log in.
I've tried a bunch of things like changing permission settings for certificates marked with a blue '+' to 'always trust' or to 'use system defaults', but it keeps telling me 'connection failed'.
I'm using an admin account so parental controls aren't an issue.
I can access App Store on my iPhone just fine and I can log into App Store using my account on other computers.
(I'm not sure if it's directly related but I also cannot update things like iTunes now either)
I can't figure out whats wrong!
Can anyone tell me what's gone wrong??
MacBook Pro, Mac OS X (10.7.4)