Built a puter for a mate of mine a few years back and he began to have similar probs,ie time and date showing silly things various bits of kit in the PCI slots not working then wokring fine at next bootup,it was the bios battery with a iffy connection,so I soldered a new one in,you could do that with motherboards int olden days.
No information at all about replacing the Bios battery in the manual which in truth does not have a great deal of information on anything.
Checked the bios for graphic boot priority and have it set for PCI Express then on board chip, actually this does not seem to make any difference,as it did not matter which monitor socket was used both work or rather should I say both used to work.