Computer Turns Unresponsive After Period of Inactivity?

This is an issue I've been experiencing ever since I upgraded my hardware (the details of which can be found at the end of the post). When I first upgraded, I had Windows XP Ultimate Edition (a cracked version with tweaks that make it faster), and I can't remember whether I was having these problems in that OS. I later upgraded to XP x64. Now, after periods of inactivity, the computer will go unresponsive. I can move the mouse, and mouseover events will occur... until I click on something, at which point everything except the clock on my G15's LCD screen will stop. Once I press an LCD control button, that screen will freeze as well. CTRL+ALT+DEL (I have welcome screen turned off) will make everything, including the taskbar and desktop icons, disappear to the wallpaper, like it's trying to show the security window, but nothing happens from there. I am forced to hard-restart my computer. This is a showstopping problem that I'm having and I can't seem to find anything about it on Google. I would prefer not to reformat, but I will if I have to.

OS: Microsoft Windows XP x64 Edition (with most recent updates)
CPU: Intel Core 2 Quad Q6600 G0 @ 2.4GHz
MoBo: MSI P7N DIAMOND SLI
RAM: 4x1GB G.SKILL DDR2 SDRAM 800MHz
Graphics: nVidia 7300 LE 128MB (Stock Dell card, I don't know who manufactured it)
Audio: Creative SoundBlaster X-Fi XtremeMusic
HDD: 2x250GB (kept as separate drives, RAID is not used)
PSU: OCZ GameXtreme 700W

Also, in case it matters, here's what software I typically have running when the system goes unresponsive:

Kaspersky Internet Security 7.0
Steam
mIRC
Google Talk
Skype
NetTime
Various Logitech Profiling Software (for my keyboard, mouse, and joystick)
DAEMON Tools


Thanks in advance,
RoFL

Probably Hibernation problem. Try disableing Sleep/ Hibernation.

Buy a real Licensed OS from M$ instead of using pirated stripped down/ infected copies.

Theres options in the bios for hibernation also.

Or it could even be a heat problem.

Try doing a Windows repair.
You could try a Linux LiveCD. If you have the problem in Linux too, it is a hadware problem.

1. Memory is just fine. It was put into my old system before I did the major overhaul with the other components.

2. I assume you're referring to PCI cards? I have not done that, but there's not a whole lot to do. The sound card could be removed, but I'm getting the Barracuda set-up soon anyway, and I have no integrated graphics, so removing the GFX card is a no-go.

3. To tell you the truth, I would rather just reformat to see if that fixes things than spend two hours trying to locate a hardware issue.

4. Link to the event log you speak of, please?

5. What other apps?

6. There is an issue I was having with my video card drivers in that the download from nvidia's website would cause my graphics to be stuck in 640x480 4-bit color. Uninstalling those drivers and using the Update Drivers button in the device manager would fix that problem, but then I'm left with old drivers... so, I don't know if that would have anything to do with this or not.

7. BIOS is v1.0 and last I checked (a few weeks ago), that was the only version available on MSI's website.