How to Reinstall Windows XP Without a CD

Over time, the Windows XP operating system can start slowing down, freezing and failing to shut down. This can be corrected by reinstalling the system on your computer. However, this can be a problem if your computer didn't come with a CD copy of the OS software (many cheaper computers won't). In these cases, there is a copy of the installment application saved on your main hard drive. You can access this software from the C: drive to reinstall the XP system and clean out your computer.

Obtain the product key or serial number for your Windows XP operating system. This number is usually located on a label on the computer frame or within its original package. If you can't find it, search though the computer's registry or contact the computer's manufacturer (not Microsoft) for help.

Back up everything on your computer to floppy disks, CDs or external hard drives. This includes not only your saved pictures, documents, other files and passwords, but also every program on the computer--especially the ones you installed after purchasing the computer.

Go to "My Computer" in the Windows "Start" menu. Open the folder for the C: drive, then open the "i386" folder. Look for the file titled "winnt32.exe" and open it.

Use the winnt32.exe application to reinstall the XP operating system on your computer. The steps the program requires are straightforward, which include agreeing to the software license, choosing the location to install the system, deleting the partition to create a new one, choosing a file system and creating a name for the computer. You'll also need to input the product key.

Reboot the system if needed. Once you are sure the entire operating system is fully functioning, reinstall or copy all your personal applications, programs and files from your backups.