Startup repair

Hello,
I am having the same startup problems as others here have - the startup repair goes through its motions and states it cannot solve the problem.

After it goes through 30 minutes of trying to repair, the computer shuuts down. I then wait a minute and restart. Startup works, but my Norton 360 has been disabled. I correct that and everything seems to be OK -- except my internet is slower and videos sometimes won't play.

This has happened on four different occasions over the past let's say six months seemingly to pop up for no special reason (as I have no MP3 or camera.