I'm looking for some advice on a problem with my home built pc (I guess it's at 3+ years now). The basic specs are
AMD Phenom II X4 940
8GB DDR2 RAM
550W OCZ Fatality PSU
(Old GPU) Radeon HD 4670
(New GPU) Radeon HD 6850
+ random bits (1 SATA drive, 1 DVD-ROM) - so the 550W PSU should be capable of handling the hungry 6850.
I've had the PC running problem free for several years with the 4670 installed. Today I uninstalled the 4670 drivers, then physically installed the 6850 (which involved a bit of reshuffling of HDD etc. in the case), but when I turned the system back on my monitor wasn't receiving any signal. I reverted back to the 4670 to check that still worked, and it didn't! I finally tried the onboard video, but that also currently fails to produce any signal. On boot up all fans (including GPU fans) fire up and run well, there are no warning beeps, nothing else to indicate any problem.
It's possible I forgot to reconnect something, but I don't see any loose wires or d/c hardware (and the case is pretty sparse, not much stuff in there to get confused about). I was slightly unsure as to how to power the 6850 directly from the PSU, but that certainly shouldn't make a difference now I'm rolling back to earlier spec to figure out what's wrong, should it??