That time I use msn the screen came up with words I did not type!!

Then yesterday the comp sot, on liao hang, on again hang, then finally cannot on!! (screen blank)
After a while can on, but hang at the start up screen.
Then cannot on again.
Then this afternoon I try the start up screen different!!

Then go to the normal start up screen.
Overclocking failed, so load default values and run..
Then finally can le.

Can someone help? I got mcafee security centre and firewall. And spybot search and destroy.
I deleted a file several days ago that could not be deleted in normal mode because mcafee found it to be potentially unwanted. So I delete it in safe mode, then my comp start acting funny (e.g start up error, log in again, they say they have a corrupted file report or what)