Computer help - locking up (Windows 7)

I have a computer problem that is driving me nuts! I figured I would post here before I take it to the Geek Squad to see if anyone here has had the same problem. Sony online helped another issue but not this one. I would appreciate any help anyone and hope that we can avoid "buy an Mac" posts and this is not intended to be a PC vs. Mac thread.

I bought a Sony Vaio laptop about 5 months ago that has worked great until about 6-8 weeks ago. I noticed that Internet Explorer would stop responding a lot and I had to close the browser down and re-open it to do anything. I figured it was a Vista glitch and so I upgraded to Windows 7 with the free upgrade DVD that Sony sent me.

The problem has gotten worse. Now, the computer freezes up when it's left idle for short while. The cursor will move (usually) but no programs respond. Ctrl+Alt+Del does't bring up Task Manager or do anything. I have to hit the power button for a hard shutdown every time.

If I'm using it then it works fine but if you walk away for 10 min, it's a gamble if it will respond when you come back.

Antivirus finds nothing.