How do you figure out that your wireless router has truly gone bad?

My internet acts slow with it. I hook my computer directly the modem, everything is fine. I restore the default settings of the router and the problem still occurs with no security. Has my router somewhat gone bad? I want to know before spending money. Its not that it doesn't work. Sometimes i will be doing something and it will just stop. or a page won't load fully if there's pictures. Its annoying at this point.