Cannot Change product Key

I had to replace the hard drive on an older Gateway E4000, it has a windows xp pro COA . I loaded windows with my xp pro oem disk, when I go through the routine of changing the product key from my OEM disk to the Product key on the COA it keeps telling me I typed an error. Called Microsoft, they verified the COA Product key and said it was valid. I have change keys many times and have never had this issue. Also, Gateway sold support for this model to a company called MPC which is filing for bankruptcy.

Has anyone ever encountered such an issue?

 

anyone? I'm stumped

 

Hello,
Use WinKeyfinder to change the key. In an admin account.

http://majorgeeks.com/Winkey_Finder_d4501.html

Antivirus may flag it but it is clean.