I do not think it is any virus/worm. Would it take 5 minutes to load windows to get to the welcome screen? I didnt think that could happen. Also, im having a problem with what i think is spyware but it is not being detected. Say a good ad comes up, it reloads where the google ad was and shows nude pictures. I have an example here but i blacked out the nudity to show what im talking about... its annoy when your browsing the internet and with your mother behind you and this happens
Im not sure if that is what is causing the lag but anything is possible
Edit: When my pc starts to lag i look at taskmanager and Cpu is 100%. Simple programs like Iexplorer and windows media player are taking 30-50% Cpu..... Its a pain.