How/why did you upgrade to Vista Home Basic then?
Regardless, the only option now is to wipe the hard drive and reinstall Windows XP from your original XP CD, your XP product key in hand. Note that this will result in the loss of all files and installed software, so you'll want to connect the hard drive to another computer and back up anything you can't afford to lose, remembering to take ownership where necessary.
I had Windows Xp and then I converted it to Windows Vista Home Basic and then it asked me to upgrade and so i did and when i had to restart my computer it asked me for my activation key which i dont have....
So now I am wondering What are my options without spending any money??????
PLEASE HELP !!!!!!!!