Unable to install window XP service pack 2

When installing window XP service pack to it got stuck on "checking product key screen"
Follow then these steps- :
1) Please go into the command prompt.
2)on c:\ type cd /d %windir%\inf
3)Then type ren oem*.inf oem*.old.
4)Then type ren oem*.pnf oem*.old1.
5)Then go to run type "%windir%\inf click ok.
6)Take the backup of INFCACHE.1 on desktop and delete it from inf folder. Reboot computer in safe mode and install Service pack 2.
Note :Please note the product key of your Window XP.
If you don't have window XP disc or don't know the product key of your window XP....Downloaded and run keyfinder to know product key of your window XP.