Windows 7 Activation key

[Fastra]

Just found out that the machine I bought from ebay a few months ago hasn't, surprise surprise, got an official version of windows on after all - it came with no install disks.

If I call Microsoft for a key, can I just enter it and carry on as normal or is it a clean install?
It's my daughters and is full of stuff I'd rather not re-install.

[Fastra]

Thanks.
Can you expand a little?
So, I can keep the system as it is?

[Fastra]

Great stuff, most appreciated.


So, just to be clear, I can call them, get a key, enter it, and my system will remain unchanged -apart from now being legit.

[Fastra]

Wonderful.

many thanks.