Okay, I'm a bit knowledgeable with pooters and such, but i'm confused. My computer is dying slowly, and I'm not sure what part is causing this.

Computer details: Vista, dell machine, intel Q6600, 2.4 Core Duo (quad core), standard memory and drive (unknown manufacturer).

Symptoms: I would best describe the symptoms as memory corruption. After a couple days on, I start getting applications crashing or failing to open for a lack of "resources". Sounds are corrupted. Onscreen text gets corrupted; the characters of text are garbled, not the pixels on the screen. Video memory seems untouched as I haven't seen any misplaced pixels.

Recently I've lost files on disk. I've also experienced errors reporting a supposed lack of disk space, even though I have fifty gigs free.

There was one point where I couldn't get to the POST when booting up. After I cleaned everything (see next) this hasn't happened.

Diagnostic steps: First thing I did was clean the case. There was a lot of dust buildup on heatsinks, so I cleaned all that up. No help. Next, I disconnected and reconnected everything, from power cables to memory (did not reseat cpu). No change. Last, I ran the standard vista memory diagnostics and ran checkdisk. Both reported no errors found. I have not run any POST tests, now that I think about it.

I'm at a loss at this point. Disk appears fine, memory too. I'd expect motherboard issues to result in the thing not booting up, yet it does every time.

What should I be looking at? What more can I do?