Windows System Restore on XP and such might be a good idea to run if you reach the point where you can rule out your ISP from the blame. Just like D3V said, it could be software-related, but undoing all of the driver changes for the past few weeks may not be the best of things to do.

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram