Control-alt-del & open process manager & look for shareaza & force it to quit. Then uninstall. Either (1) you have Shareaza set to start at system startup or else, (2) you have a virus that's been going around that gets into the startup items & makes the program start up at system start up & keep opening after closing. If that's the case (point 2), best answer is to visit & register at this site:
NorbiesWorld (click on link) & follow the instructions carefully with posting a report. Norbie "is" an expert & will help you clean your machine.