Ip address problem-need urgent help

Hello,
I need to sign up for certain websites which require one sing up from one IP only. I have recently taken an IP for my connection and I have not signed up yet but it shows that there has already been a sign up from this IP.
I do not understand why this is happening. Kindly inform me if there is way to solve his particular problem and help me get this IP work.
Matth Santos.
