Windows XP PRO SP3 Issue

I have a OEM Copy of WIN XP SP3 which was provided to me by the store who built a PC for me about 3 years ago. I wanted to install it on one of my systems, but when I call to activate, I get the message: this is not a valid product. It IS! Valid, as I activated it some time ago, I called Microsoft Tech Support, and they asked me to confirm the CD Part Number related to the Product Key. They then told me the product key did not match! It was a valid key however for SP2 not SP3 I'm totally at a loss as to what the hell has happened, but I still am unable to Activate what is a clearly legal and genuine copy of WIN XP PRO SP3, I dont have a SP2 CD btw.

 

"Maybe" the store installed from an XP/SP2 disc & then installed SP3 afterwards ?

Any chance of asking the store to sort it out for you, if you can't ?

I've installed & reinstalled the SAME XP/SP2 OEM disc Several times on this comp & on a previous different comp/motherboard i also built. Every install has worked fine & i was able to register automatically via phone to MS each time.

Hope you manage to sort it.