My computer is messed up,please help me,what should I do?

Well see,I downloaded limewire just the other day,but I guess that messed my computer up,the thing is whenever I log onto my computer,the desktop appears,then dissappears,then reappears,continusiously,or then it just dissappears...&& dad got pissed off at me cause I messed it up,does anybody know a way I can fix this?