My DSL internet is so slow that it is barely usable?

Youtube, Google and Netflix video is so slow it sputters and stops. Links on email and web pages routinely do not work. Even closing out pages mostly does not work. I just got my computer "fixed" but now it is the slowest it has ever been since I bought it five years ago. Are there any concrete steps I do do. I am so tired of having to fight this computer to do simple things. I have started using Firefox but it's linking to other web sites and browsers is just as slow. Please help.