windows xp install/uninstall problem

[CorpseFire]

Tonight i tried to install windows xp home on the computer i just built, i got as far as the prompt to enter my cd key. it was only then did i notice i had lost my cd key so i exited setup and shut down the pc. A friend of mine came over with a copy of windows xp pro that he doesnt use however, i cannot get it to install because the windows home is partialy installed already. All i get is an error message with no options other than to re-boot. How can i overwrite the origional install? is there a way i can delete it through bios or anything? thanks in advance for any help.

 

[Zoron]

Delete all partitions on the hard drive and start over. You'll be presented with partitioning options before Windows actually begins installing.

 

[CorpseFire]

I dont see where I can delete the partitions, it never gives me the chance. After the screen where you would enter bios passes it goes straight to windows loading screen and then i run intno the dead end because i do not get any options to exit, cancel or delete the origional (incomplete) install.

 

[Zoron]

Then go into the BIOS and make sure your CD-ROM or DVD-ROM or whatever is set to boot before the hard drive. Sounds like it's not giving you the option to boot from the Windows CD.