Your PC ought to have had a restore disk with it or an OEM Windows disk (with the correct drivers).
You can try a repair with an XP disk - anything can happen - but if the PC can be online at the same time, then it can try and find the right drivers if necessary from the web.
But you have to get to the root of the problem. Something has destroyed a sector or block; either hard failure or corruption by a program.
With the XP disk you can at least boot to the command console (yes?). If you can't then you have a physical problem on the disk, I'd say. If you can, you'd want to run CHKSK. First without /F paramater so that you can assess what might be destroyed by /F. /F is supposed to mark bad blocks and repoint the disk block chain. But if the block is in the boot sector, you're going to have to FDISK the drive using the /MBR option to rewrite the boot sector; then format the drive and set Windows up again and hope that your internet access in the boot process can get the right drivers down.
Do search for a restore disk please. Some manufacturers put the recovery stuff onto a D: partition - quite useless if the HDD goes down.
Keep us posted.