Cant boot up my computer, says I need to activate windows...help!

[Drex]

So I have win XP professional and I installed it about a month ago. When I boot up as windows is loading it stops and tells me that I need to activate windows before I can log in. So I click yes to activate and nothing happens, it just sits at the log-in screen. I try to log in and I get the same message telling me to activate. I even put the CD in the drive and nothing happens. Anyone know what the problem is? Using someone elses computer to try and figure out what the deal is here...