Virus wont let my computer open spybot search and destroy?

A box keeps popping up telling me that google toolbar user_32.exe can not start it says it is infected by w32/Blaster.worm. Ive tried to set it to safe mode and use spybot search and destroy but then when i put it back to normal mode the pop up shows again. I tried downloading other spyware or malware removal programs but it wont let me download any tools like stinger or symantec worm remover. I dont know what to do as im not that familiar with computers. I have mc afee but it wont pick it up for some reason. please someone help?