|"The system boots fine with all drives attempting to be accessed, but no video signal"|
If there's no video signal, then it doesn't boot fine.
"I have installed new and tested Pci-x video card"
I highly doubt you have a PCI-x video card. If you do, maybe that's your problem...lol
"Not to be confused with PCI Express (PCI-E or PCIe), a different bus architecture"
"The only thing that I can think is to install new bios"
It's not a BIOS problem.
When's the last time the system worked? What did you do since then that may have brought on the current problem? Did you make any other hardware changes besides adding a "PCI-x" card? How did you test the PSU to confirm it's good?
"No original boot disks either"
What do you need boot disks for? If you're not getting the POST screen, it's a hardware problem, NOT a software problem.
BTW, what does any of this have to do with CPUs or overclocking?