if your screen is sliding over, it's likely your monitor, not your PC. What type of monitor do you have.
Slide over to www.windowsbbs.com
, they have a great windows support forum there where they will walk you through diagnosing your system. They are great!
Or just PM me and I can walk you through it all. I work in IT so I'm used to it. Do you have MSN Live? there is a feature in it that will allow me to remote into your computer desktop so I can see your computer and access things. We use it in IT all the time (not MSN Live, just a different program that does the same thing). It's very useful because we can "see" the problem, instead of just having it described.
I bet you just need routine maintenance done - AVG virus scanner, Zonelabs free firewall, clear out unused files, adaware to remove spyware, remove unwanted software/bugs, defrag, scandisk, stuff like that. I do that once a month.