If u are using a windows disk Which came with your system then this problem should no arise, but if u are using another disk and just putting the key to activate it will not go like that,u need to have a OEM disk from the manufacturer of your system, because
every manufacturer have a specified number of keys registered to them , and they cannot work with installation from other disk than their own OEM disk,i.e if i have a OEM XP disk of Sony the key for Sony will not work in Dell's OEM disk it will only work on
Sony.
if u have a retail disk then u should have a retail key to instal it, OEM XP key will not work in Retail XP disk
How to :
1.Select the right version of disk from OEM or Retail
2.Use phone activation :
866-542-3062 (http://www.contacthelp.com/directory/Microsoft?ListingID=224) copy this link and see it
3.If your key is genuine you can apply to Microsoft to issue a new activation key by giving documentation like purchase receipt of system and a picture showing the serial number of your system and the activation key in a single picture, the activation
keys are provided in back of a system near your systems serial number.
4.You can also apply for refund of the Operating system at the price of today's date see Microsoft return policy
