Why is my computer so slow??? even after a complete system recovery?

My laptop started giving me problems a while ago, it was running slow (particularly internet browsers, but other things as well). Ex. Firefox would stop responding, and i would ctrl+alt+del and then it wouldnt close; same thing would happen with safari.. my computer started running slower a little before this, and it seems to run even slower after programs stop responding, even if i close them out... So, i did a system recovery to put it back at factory settings; and i am still having the exact problem......... Can someone help me? I really don't want to buy a new computer unless its absolutely necessary.. Thanks.