what im about to ask might sound really weird when you read it but please try and help me cause im not a wizard at all this internet stuff

I've had ntl broadband for 2 years nearly and apart from a few minor connection problems it has been very good.... until 6 months ago when on my old computer it started acting up a bit. for example: when using the internet i would click on a link and the loading bar would start moving very slowly. There would then be about a 5 second pause while none of the sending or receiving lights on the modem itself flashed. Then, all of a sudden it would spaz out (I'm sorry i couldn't think of a better way to put it!) and in an instant the page would load!

I thought this was just a problem because of my computer being old but now i have a new shiny vista machine with the same problem. The broadband was like lightening at first but now has resorted to its old trick of doing nothing for a while and then loading very fast. I should add that i have a linksys wireless-g router but this problem had already begun before I installed that about 6 months ago. I currently have no antivirus installed, only windows defender.

Sooo... has anyone else had this problem or know how to solve it??