Not accepting my activation key

[simonjs]

I did a clean install of W7 and moved from 32 bit to 64 bit after entering the my genuine Key which I assumed was accepted .
Now a week after a pop-up key activation window has appeared telling me my key was not accepted and to enter a valid one.

I bought my T510i with windows 7 pre-installed so I don't know what happened, I've checked and double checked my Key and it still keeps coming back!!

[emtee3511]

If you right click on the computer icon and choose the Properties tab, what does it say at the bottom of the Properties window under "Windows Activation"?

[simonjs]

Thanks, before i saw this message i went to system and re-activate product key, this time it was accepted.

It now says "windows activated"

Not that it matters but my OEM number seems to have changed after the clean install.