XP MCE login real product verification

OK. My HP fried hard core durring a lightning storm. I brought it to a place to fix it. He could not. He installed all new components. Now I have a Dell in an HP case. When I got it home, this was about 3 weeks later after the fix, the Windows login comes up and I say “OK”. It then wants to verify that the copy is authentic. It runs and says “ok your copy is authentic”. Brings me back to the login screen and does the same thing over again. When I was on vacation for the three weeks he went out of business!!! UGH!!
I’m caught in a catch 22 with this machine. If it’s “authentic” why does it keep asking?? I don’t want to go buy a new copy of XP. For that price I could go buy a new PC and put all my parts in the new case.
What are my options??? Please help.