Random Crashing No BSOD

My computer has been randomly crashing. The crashes are kind of strange... The audio coming out the speakers studders, then the mouse stops moving, and then everything on the monitors stop moving. No blue screen and it doesn't unfreeze even if I wait a long time (20-30 minutes). I have to do a hard reset to get the system working. The crashes typically happen soon (5-10 minutes) after I start the system, but can happen at any time.

I reinstalled windows, installed every windows update, installed all of the latest drivers listed on Gigabyte's website, flashed the bios, and the problem continues. Nothing is overclocked except the GPU which is factory overclocked. I've got all of the cables tied down and tucked away, and the air flow feels pretty good. I've run all of the diagnostics that I know of and nothing points to a problem.

System Specs:

OS: Vista x64 Ultimate
Motherboard: Gigabyte GA-EP35-DS3P
CPU: Core 2 Duo E6750
Cooler: Zalman 9700 CPU (With Arctic Silver)
Ram: 4x G.Skill 2GB PC2-6400
GPU: MSI RX3870X2-T2D1G OC Radeon HD 3870 X2 1GB 512-bit
OS Drive: Western Digital Caviar 250GB (wd2500ks-00mjb0)
Swap Raid: 3x Western Digital Raptor 36GB (In RAID 0 using windows software RAID)
Wireless card: EW-7128g
Power Supply: ZALMAN ZM750-HP 750W
Optical Drive: LG gsa-h62n
Case: RAIDMAX SMILODON ATX-612WBP (With the door on the front removed for better air flow)
Monitor: 2x 19' Hanns-G LCD

Any ideas? I've tried everything that I know to do.