matrixlu :
just an info. If you had been hacked, changing ur IP will probably change nothing (ever heard of zombies).
net security is maybe not a great subject of interest 2 u, google zombie if u wanna leran more!
To tell u simple things, when u r connected to the world wide web, generally ur ISP assigns u an IP address at each connection. So betwenn to connection ur IP may b different.
So forget about it!

The real question is have u been infected: There are many cleaners or detection system available for free on the net. Have a look on AO archive forum & u'll find one.
After that if u fell concern about ur puter security u should think about firewall, IDS, logs etc, ... etc and participate on AO forum to learn.

godd luck