Dell :: Studio 1558 Freezing, Unresponsive

Had this Studio 1558 for about a week now. It's been mostly good, except it's been freezing for no good reason every so often. I'm not getting error messages, BSODs, automatic restarts, or any of that. The screens just stop responding.

I suspected it was a bad Win7 install, so I wiped and reinstalled Win7HPx64. Still froze.
Went back to a single-monitor setup, still froze.
Tried updating to the Catalyst 10.04 drivers, still froze.
Disabled Powerplay, still froze.
Changed AV/Firewall and uninstalled a pile of crap, still froze.
Installed XP, then Ubuntu, still froze.

Odd thing? Nothing in the event viewer to indicate a crash, other than the fact that a kernel power error shows up because I force a shutdown. I've yet to find a .dmp file anywhere that would indicate an actual BSOD. Fan never spun up, CPU monitors and logs don't show any sudden spike or drop in processor activity. Think the 4570 is busted?

*edit*
just recalled, I've also changed power settings so the CPU can't throttle, been monitoring all 8 cores, ran off battery and off ac, all to no effect.

happens whether i'm streaming video via hulu desktop, just browsing webpages, running virus scans, or just doing mostly nothing. ran the gamut of dell diagnostics, but nothing.