LR, does the HP have a sticker on the case with the product key on it? Does it match the product key shown on start>computer>right click "properties"?
If yes, you may have been hit by a known problem where the BIOS SLIC can't be read for some reason. This may be listed as the cause in the diagnostic report.
I do know there was a KB fix some time back for fixing this problem on (mostly) HP computers, and a separate fix for recovering from it if you'd already got the problem, but I can't remember where/when I saw it.
Otherwise, you can revalidate by changing the product key. I don't know Vista, so if there isn't a button on the screen to change the product ID, you can enter "SLUI 3" in the start>search box to fire up the right program.
It may require talking to a yooman bing at Microsoft.
Last edited by Bushfiva; 6th Mar 2011 at 08:34.
Reason: E&OE if this breaks things even better