xp issue, please help

My gf and I took her mom's old computer tower, it already has windows xp on it but when you start it up it goes through everything and then a message comes up that says windows needs to be activated, do you want to activate, click on yes then i get another message that says that windows is already activated, it then takes me to the log on screen and my gf's step brother was the only one that used it so I click on his name and then it tells me again that windows needs to be activated and then goes through the same cycle. What could the problem be

 

there could be an issue with your startup program what is your computer starting up with in the msconfig system

 

i have no idea, I can't even get there to check, i can get as far as the log in screen and then it tells me that windows needs to be activated

 

Seems like you may have to find your moms disk, as hardware may have added or taken away. this is a normal pain in the arse. with the key you will be able to resolve though Via telephone, Possibly your mom used her old winows XP on her new PC? Microsoft sees this and wants you to now shell out cash for your own copy?
Jaza