I have a pirated Windows Xp installed in my pc but
Okay, first things first- Pirated versions of software simply ain't cool, for any number of reasons (first being that using pirated software is ILLEGAL!), but in addition, most pirated garbage has all kinds of extra junk with it, like trojans, viruses, keyloggers, etc. which may be preventing you from installing a proper OS.
If you know what kind of harddrive you have, go to the manufacturers' site and get yourself their version of disk management software (usually a self-extracting .exe file that'll write to a 3.5 floppy). Make sure you get the version applicable to your particular drive. Make the floppy, and restart your computer with the floppy in your a drive, and follow the prompts to reformat the drive (bear in mind that you're going to lose everything on the drive). Remove the floppy and shut down your computer.
Next, restart your computer and get into the bios settings, and set your boot order to read your optical drive (CD or DVD-Rom) first, save settings, put your OEM disk in the drive, and restart- You SHOULD be good to go.
Another note: If your OEM disk isn't from the manufacturer of your computer, you'll still have issues, as OEM versions are coded for particular board/hardware combinations.
Bottom line- Computer systems are becoming more and more affordable, and using pirated software only leads you down a path to problems. Reformat your harddrive and open your wallet enough to get a legitimate copy of the software you want!