I often work with Z800 workstations. I upgrade them with x5670 processors and populate it with more RAM, for nice workflow. I have noticed one strange thing, which at first I thought was the issue with the fact that they are upgraded with the different processors. but turns out that very often this happens with the original processors too.
SO the issue is: after a restart computer would not boot. It powers on, fans start spinning louder then usual after half a minute, HDD LED will not show any progress, no beep codes, and nothing on displays. Solution for now that worked (but not for long) is when I force to power it off, drain the power and reset the CMOS. After that procedure It would start up and sometimes after 2nd or 3rd restart it would not boot again.
I have 3 towers now with GTX 570
48GB of RAM (6x 8GB 133MHZ Registered RAM, installed in 1,3,5 and 1,3,5 dimms)
Processors: Dual x5670 and one tower with Dual E5640
Windows 7 OS.
BIOS v3.61 (which is latest)
Power supplies: 850W.
If anyone had same issues, please share how you battled.