Well I don't think that updating the firmware would do any good for this issue, but on the other hand, it can't hurt either. Just don't use this computer for that, as when something goes wrong while updating, you might be in trouble.
Other factors than the mainboard? Could be. As I mentioned, the cabling is one of them. Can be other things as well (like the PSU), but it's not very likely. Still, could be.....
If you want to make sure it's not software related, you should boot to a non-Windows environment. Take a CDROM enabled DOS bootdisk, a Win9X installation disc or maybe a live Linux distro to boot and see what happens. No problem there, then there is something wrong with Windows. Otherwise it's hardware.
Go to http://www.download.com for a bootdisk or to http://www.knoppix.org for a bootable live Linux disc.