Windows xp saying key isn't valid after fresh install?

I bought my computer 3 years ago. All I got with it was an acer recovery cd and system cd, no actual xp cd. I really needed to do a fresh install and format my hard drive, etc because my computer was overloaded and too slow. I used my mother in laws cd and the product key from my computer. I found it through a program online that tells you all of your system specs. Anyway the install went great but when I try to register online (it says I only have 30 days to register so microsoft can prevent piracy) and use my product key (not my mother in laws of course!) it says it is invalid. What is going on? I refuse to buy a new copy of Windows XP since it was installed on my computer when I bought it. Any help is greatly appreciated! Thanks

I'm not sure about this but my guess is that because the key that was on your computer was for a bundled version of Windows, it will not apply to a stand alone version, even though the operating system is essentially the same. You should probably use the system restoration CDs to restore your computer.

If that is not an option, it is possible (albeit illegal) to use your mother in laws product key on a second computer. As long as she hasn't reinstalled recently, Microsoft will probably let it go through. To my knowledge, Microsoft cannot track how many computers a key is on, only how often the key is used to activate Windows. I reinstall Windows every six months or so and never have an issue with reusing the key. However, if I try to reinstall twice within a short period, I have to call in and explain why.

Please keep in mind that using your mother in law's key is technically illegal, even though you already own a Window's license. And I cannot guarantee that Microsoft will not find out.

buy another one

Call Microsoft. they will be able to check and see if the product key used is a pirated copy that is going around....

if so they may offer to walk you though changing it and then activating windows, they may also just tell you that you need to get a valid copy of windows...

You didnt hear this fomr me but
>.>
<.<
download a pirated version

Try using a different CD and cd key......gud luck

Please visit http://www.microsoft.com/genuine/default...
and here proceed to install the small file that will do the rest
make sure that the pop-up blockers and disabled,
Good Luck