Start wont load window, just flahing light on screen. may have got virus

When you say "just flashing light on" do you mean the monitor is on but the screen is blank? When you turn on the computer does it boot at all; does the BIOS start? If not look and see if the green LED on the motherboard is on. If it is not on then you may have a power supply problem.
If the light is on but the computer will not power on then; turn the power switch on the back of the power supply off and wait a few seconds and then turn it back on. When you turn the computer on; look at the fans on the power supply and processor. If the fans turn on then turn right back off; I would say that your processor is bad and you need a new processor.

Remove hard drive, find out make and model of hard drive. Go to hard drive manufacturer's website and download testing software (if you have another computer with internet access). Should be a bootable ISO file. Burn the boot cd and run it on the host computer after reinstalling the hard drive. Sounds like a bad hard drive in my opinion.