Have you tried stopping it in your task bar, RIGHT CLICK START MENU. TASK BAR, CUSTERMISE, Limewire should be in there disable it and reboot your computer.
Have you tryed ending the process in Task Manger to kill it completely? If it pops back up, possibly one of your settings like blackjack said, either that or a possible virus. Gotta be careful with Limewire, I myself have had no problems with it, but you have to be careful what you download.