Windows 7 - System hangs "randomly", locks out CTRL+ALT+DEL

Hey guys. I've done a ton of Google searching and troubleshooting on this, to no avail. At first I thought it was Flash (using Firefox), but have since had problems outside of Firefox, using basic things like Windows Explorer, Google Chrome, whatever.

The computer hangs, programs become unresponsive, sometimes gray out. If I wait 10-30 seconds, it comes back and is fine. This happens probably once every 10-20 minutes.

Here are my specs (via CPUz):
CPU: Intel Core 2 Duo E6600 2.4GHz 32-bit
Mobo: Gigabyte P35-DS3L Rev. A2
BIOS: Award Software International, Inc. Ver. F9 Date 6/19/2009
Memory before upgrading: Kingston 2GB (2 x 1GB) Hyper DDR2 KHX6400D2LLK2/2GN
Memory after upgrading: G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-4GBPQ
GPU: Radeon X1950 Pro Rev. 9A 512 MB

I've done all the virus/adware/defragging/Windows upgrading. I was reading about the BIOS updates on my mobo, and noticed one mentioned fixing PS2 keyboard support. I was using a PS2 keyboard, so I swapped to a USB keyboard and was still getting the hangs. I flashed the BIOS anyway, to see if the newest version helped, which it hasn't.

I then thought it might be the memory, and I could use the upgrade to 4GB anyway, so I bought the G.Skill memory which was highly recommended on NewEgg. It's not on my motherboard compatible memory list, but I thought I'd take the risk since it has a ton of great reviews. Put the new memory in, and it hasn't helped the hangs.

It doesn't seem to be a software thing, since it happens in different software, and I tend to take pretty good care of my computers and don't get a ton of viruses or spyware. My other thought is that it's the motherboard, but I want to see if it's something else before buying a new mobo.

I can run whatever scans that helps people identify problems, just have to show me where and give me some directions. Any help on this is very much appreciated.

Edit: I ran MemTest86 with no errors on the first set of RAM, too. Also, if this should be in the "Crashes and Debugging" forum, feel free to move it there, sorry about that; new to these forums.

I would run check disk, with scan of bad sectors selected. Does it hang on start up ever?

Check disk didn't catch anything. :/ Doesn't really hang on start up. It seems to have gotten a little better since installing the new memory, but it's not completely gone.

How many passes of memtest did you run? did you run one stick at a time? and try the various mobo slots? that sounds and feels like a memory issue. the "greying out" especially.

Let us know if you need help

Ken

I ran it twice on the old memory, wasn't sure how to run it on one stick at a time, and didn't think to try different slots, I'll try to get that done today and see what comes out of it. Thanks Ken!

This just happened after a game of Starcraft 2 crashed out on me. I'm not sure exactly what the RAM peaking like this means, but I don't think it should be a RAM issue since I just bought the new 4GB of memory. Twitpic - Share photos on Twitter

Another thing that I noticed is that while I'm in Starcraft 2, my computer will beep at me, and it seems to be correlated to the graphics giving out? I would think my Radeon X1950 Pro would be able to handle it at least decently, but maybe it's a graphics card thing?

Is this what the computer beeping means? Why is My Computer Beeping? Yikes! Any ideas?

beeping most often occurs when hardware is not completely plugged in (memory, video cards, ect), and especially when your computer is over heating. In most cases of over heating though your computer will usually just freeze completely. Take apart your case and make sure everything is snug is all I can suggest at this point.