Windows 7 - Intermittent Freezes for 5 to 45 minutes

I have a problem that leaves no errors or logs (that I can find):

I rarely turn off my computer. My monitor is set to turn off after 15 minutes of inactivity, but all other power and sleep options are disabled (no screen saver, never sleep, never turn off hard drive, etc.).

About once every week or 2, when I come back to my computer and move the mouse, the monitor comes on and I can see the desktop and icons. I can move the mouse. But the windows that were open when I left, are not showing, the taskbar will not pop-up when I move my mouse to the bottom of the screen (I keep it hidden), and clicking on icons does not select them.

In short, the computer is "frozen". However, my clicks and keystrokes are cached and after anywhere from 5 minutes to 45 minutes, the computer suddenly "unfreezes" and processes all my clicks and everything is fine. It's as if all background processes are running (I think), but explorer.exe or desktop window manager is frozen... I don't know...

I have scoured Event Viewer and found nothing. I have tried to leave Task Manager running but when the "freeze" occurs, all the windows are hidden and I can't see Task Manager until the computer "unfreezes".

I usually leave Outlook 2010 and Chrome open when I leave my computer. I did notice once, that even though I could only see my desktop and icons, my mouse behaved as if the Chrome website that I had opened was actually appearing on the screen (as I moved the mouse around my desktop, the arrow would change to a hand in certain spots - as if I was hovering over a hyperlink on the page that would be showing. Once Windows "unfroze", Chrome appeared and the hyperlinks were showing in those places where the hand was appearing - not sure if I'm explaining it well).

Any ideas how I can get a report or event or log to see why the freeze and unfreeze is occurring? I think it's only happened when I come back to my computer after the monitor has turned off, but then again, only 2 or 3% of the time... but very frustrating when it does happen.

Thanks!

Specs:
Windows 7 Ultimate 32-bit
2GB RAM
Intel Core2Duo 2.4GHz
VisionTek X550 PCIe 256MB video card (Microsoft drivers)
Abit AB9-Pro Motherboard