BIOS question

I've googled "bios virus" and there seems to be a split decision on how virii affect bios. Some say a virus cannot exist in bios - an external virus just scrambles bios data. Others say it can exist inside the bios chip. With that being said, here's a few questions:

- If the virus can exist inside bios, how does one delete it? - Does "restore bios defaults" correct an scrambled condition? - Would a weak battery affect bios stability or is it just for the clock? - If the bios virus checker is enabled and a virus is "detected" just prior to booting into DOS, does a virus probably exist?

The problem I'm having is I cannot load an OS onto a hard drive. I get random error messages that are totally unrelated. Sometimes I can boot to a bootable floppy but cannot change drives. Other times the boot process freezes. The HD has been reformatted and is clean. Two different OS's on two different CD's act the same - the loading process starts but early into the process messages about missing or corrupt files stop the loading. Like I said, symptoms are random on most every boot, which leads me to think bios virus. Any thoughts?

Bob