Freezing Issue with Dell Precision 690

I'm having weird freezing issue with my Dell workstation. This issue presents it self even when computer is under heavy load or no load at all.

Everything freezes in an instant, moving the mouse, the laser light under turns off, touching any key on the keyboard the lights go off, power is cut to all USB components. At first I thought it could be driver issue but I've updated all the drivers. I've tried it with different operating systems, switched out the CPU, changed the memory, changed the hard drive and still the issue persists...

I'm wondering if there is a program/tool for testing bad components or if anyone has any ideas it would be much appreciated...

Thank you,

Dell Precision 690, (2) Dual-Core 2.66, 16GB's FB-DIMM, Vista 64-Bit, 150GB Raptor...