1720 harddrive failure

Check all cable connections.

Is it a desktop or a laptop PC? If it is a desktop PC, you could try swapping the hard drive controller card, or installing a controller card if the controller is on the mother board.

I would run a disk utility such as SCANDISK or Norton Utilities. Fix any errors on the hard drive. Then try booting up. If it doesn't work this time, you probably have a bad hard drive or drive controller. To test which may be bad, try installing the particular item in another computer, to see if it will work there, or if the problem continues. In fact, swap drives and controllers with a known good PC. You'll know whether the drive, the controller, or something else (e.g. the motherboard or the cable) is bad.

Good luck.

Try booting up in Safe mode. You could have a driver/software conflict. If it boots in safe mode, go to device manager and remove all devices that are not currentl installed. This has worked more than once for me. If it won't boot in safe mode, try removing (physically)all cards except the vga card and the ram and try safe mode again. Good Luck!