Your ISP issues your IP address, it is not under your control.
Which ISP do you use?
Most ISP's give out different IP addresses every time you connect.
To check this, connect several times, and open a DOS window. (start, Run cmd.)
then type ipconfig , and hit return, and you will see your IP address in the form 123.456.12.456
Try this after you have connected several times. If the IP address is always the same, then you need to contact you ISP, for them to stop you having a fixed IP