It says my windows is not genuine

I have been using Windows XP for about a year or so. I installed it using Dell OEM that I paid for, it's UK version. Soon after installation, a genuine check was made and it did pass. I got frequent updates including an update to SP3. Recently genuine checks started to say otherwise.

I ran MDADiag and it gave me "Validation Status: Geographically blocked PID". I live in England, UK.

This is the result from Microsoft website:

It looks like my product key has been stolen by some program or there is a misunderstanding somewhere in the validation process.

I don't remember where I kept the CD but I have not shared it with anyone. My computer is still working smoothly, only sometimes it fails to shutdown. After the incident, I installed and ran AVG and Registry Mechanic to clean my computer but that didn't help the genuine problem. Is there anything else I can do to clear it up? I am very unwilling to buy another copy or pay £95.86 seeing the problem will likely occurs again.

 

Start here http://www.microsoft.com/genuine/
I click Contact. Numbers are given for the US. I assume since you are viewing from the UK, the contents will change.
If you do not see a toll-free phone number, email and tell them what you have posted here.

The validation is not 100% foolproof. Find your CD and sales receipt so you can supply the information.