Internet running very slow

Hello,
Ok so I tried the Firefox installation and to no avail. I can't even get on to some websites. When firefox doesn't load a site it says: "This site could be busy or temporarily unavailable. Try again in a few moments. #2 If you are unable to load any pages, check your computers network connection. #3 If your computer or network is protected by a firewall or proxy make sure that firefox is permitted to access the web. I was having problems with IE that's why I switched but still having problems with even viewing any videos at all they just dont run or run a second and take 15 to load the next sequence. Everything has been erased in my cache for cookies, checked for viruses, it suddenly did this starting after I was playing some long winded youtube videos. I changed nothing in my settings except opening my firewall so. Any help ladies and gentleman I don't need to spend any more money on this labtop.