Lostproduct key

Hello,
I'm having a little trouble getting onto microsoft office word 2007. I have a gateway laptop with windows vista and whenever I want to type something, I have to type it in notepad(very annoying since i cant copy and paste pictures on there). So, when I first got my computer(6-8 months ago), it worke fine for about a wek or 2, then it says "Although you are not required to enter your product key now, we recomend you do so for ease of validating your microsoft license." every time I open it. The laptop came with microsoft word, I didn't upload it from a cd. So I need help finding my lost product key.
thx)