My computer is slowing down*

Hello this is Mike from houston, you got a nice forum here with some good topics and I hope you can help me with some tehnical problems* Im getting a lot of popups when Im browsing the internet, sometimes even when Im not at the computer, I leave it on for an hour and when I get back I have 2-3 popups that have appeared from nowhere. How can I remove this? Im really not intrested in finding adult friends or downloading a new screen saver * Please help me, Im kind of low on budget and wouldnt like to take the computer to an expert and pay a lot of cash for it, all the ideas are welcome and I will definetly try them! Hope to hear from you soon!*