Assuming Windows XP?
Have you got an XP cd?
1. Boot the computer using the XP CD. You may need to change the boot order in the system BIOS so the CD boots before the hard drive. Check your system documentation for steps to access the BIOS and change the boot order.
2. When you see the "Welcome To Setup" screen, you will see This portion of the Setup program prepares Microsoft Windows XP to run on your computer:
To setup Windows XP now, press ENTER.
To repair a Windows XP installation using Recovery Console, press R.
To quit Setup without installing Windows XP, press F3.
3. Press Enter to start the Windows Setup.
To setup Windows XP now and Repair Install , press ENTER.
Choose "To repair a Windows XP installation using the Recovery Console, press R", (you want to load Recovery Console).
Select your Windows installation, then type the administrator password – press Enter if there isn't one.
Now enter the following commands:
recovery console will run a disk check on your drive and hopefully fix it. When completed type
remove the cd and press enter
the machine should then reboot into windows.