Crash troubleshooting help

I've had a really nice build running for about 3 years now. About 3 months ago I started having random crashes while playing games. A hard crash where the screen turns black or has bars and some obnoxious sound plays through the speakers until you hit the reset button. After one of these crashes my video card would no longer show an image after several reboots. I could tell my computer was still going through the boot process since the HD was being accessed and the Windows start-up sound played. So I replaced the video card with a new one. That helped with the crashing somewhat, but I still get hard crashes sometimes. I also replaced my PSU about 6 months ago, so the one I have in there is fairly new.

My system is substantially OC'd and overvolted so I tried restoring stock settings for a day but still managed to get the same type of crash. The video card however is stock speed and voltage.

I usually get a new PC every 2 years or so, but I really liked this build and I'm reluctant to change it substantially. It has been the most stable system I've built even though it's been OC'd since the day I built it. But now I wonder if that hard usage has taken it's toll on the capacitors and everything and maybe it's time to build a new one?

System:
ASUS P5W DH Deluxe
Intel C2D 2400@3400
Corsair XMS2 2GB DDR2 800
EVGA 8800 GTS (dead) ATI Radeon 5770(replacement)
Hiper 580W PSU (dead) Antec Truepower 550W (replacement)

Cleaned out all heatsink/fans and ensured that the MCH/ICH's are cooled sufficiently?

Use the Manage Attachments button and give us your five most recent minidumps. You can easily zip them in one file and I'll attempt to read them.