Firstly, suspect your problem to be a hardware issue. The graphics driver is not applied and utilized during post. In fact, none of the drivers are loaded until after POST.
POST is self dependant on the BIOS, nothing more. So even if you don't have a Hard Drive drive connected to the PC, meaning no Operating System, then your PC should still be able to carry out POST. It is after POST where BIOS searches for a bootable drive with an Operating System, then loads the OS and the drivers for devices.
During POST you should still get a display. The only type of virus which can cause boot problems would be a boot-sector virus.
Suspect your graphics card first. Make sure it is compatible, working and in place. Cables too. Make sure the RAM is correct and that it is seated correctly (you might want to shift them to different slots). Probably the most vital item to consider is the CPU. Check to make sure there is one
. that it isn't fried, no pins bent, is in place and working. If all of this is checked, then most probably some issue with the motherboard.
It's a tricky problem, but sounds completely hardware based.