activation key problem

Two days ago I was using my computer and it hang up,nothing strange,reseted
it and oops: what's this message asking to enter my key to activate windows?I
took a look on the case sticky and entered it down but it tells me that its
not an authentic key (god it's a sticky of Microsoft itself ) how this could
be?
Im really disappointed please help I dont have much time:it says 12 days
left !
I have an Intel e4300 based comp with 2 g sys ram a geforce 7950 512mb
Kaspersky Antiv 6 win Vista home premium w: all updates from microsoft.
all worked fine aboout 1.5 month then booom!!!!!!!!!!!!!!!!!

----------------
This post is a suggestion for Microsoft, and Microsoft responds to the
suggestions with the most votes. To vote for this suggestion, click the "I
Agree" button in the message pane. If you do not see the button, follow this
link to open the suggestion in the Microsoft Web-based Newsreader and then
click "I Agree" in the message pane.

http://windowshelp.microsoft.com/com...unts_passwords