Unless you did something to your computer that changed your internet connection settings, this problem might be with your service provider. You could try using a system restore point that goes back to a date/time prior to when this problem first started. System Restore
If a system restore doesn't help you can undo it if you want to. System Restore - Undo - Vista Forums
(same tutorial works with Windows 7)
Personally, I would contact customer support for your internet service provider. They should have the tools to run diagnostic checks on your computer and their own service.