If you can't boot into Windows at all, then follow this paragraph
When you start your computer , just after BIOS checked your hardware, press and keep pressed the key F8. Eventually you will see menu which will ask you which mode you want to use. Press "r" for recovery mode. If you can load Windows but things aren't working quite right, then follow these steps: Click Start, All Programs, Accessories, System Tools, System Restore, and choose "Restore my Computer...." The System Restore feature of Windows XP is used to return your computer to an earlier saved state without losing any data files if you have system problems or other failures with your computer. System Restore will take an image of your computer at a given place in time and save it as a restore point.
There are various ways through which you can repair Windows XP. You can format your device and reinstall the software or use the system restore function in the operating system.
There are several ways to get to the Windows XP system restore. The easiest way to do so is by going to the help center in the control panel. Another way to access the system restore feature is by booting the computer with the Windows XP CD.
It allows you to restore your computer to a previous state incase of a system problem.
restore
system and registry settings
Go to "Start", then into "All Programs", then into Accessories, then System Tools, then click System Restore, then follow the on-screen instructions.
Windows XP and Windows 7 both use the same file system by default: NTFS.
Operating system CD
If you have windows vista, click on start and type 'system restore' in the search box down the bottom and click on system restore when it appears If you have xp, click on start, All programs, Accessories, System Tools and then system restore. I'm not sure about windows 7. (Any version of windows which is 98 or under will not have system restore.) Hope this helps!
You can reset the Windows XP by performing a Restore operation.
You use My Computer & Windows Explorer to browse the file system on a drive in Windows XP.
Restore point