Sorry to hear about the problems with your compute.,
1 Is the operating system ands your software all legal and correctly licenced?
2 When you formatted did you use a Restore Partition or a DVD? (if DVD is it a genuine Microsoft installation disc with hologram, or is it a copy?
3 Did you get the problem immediately when you had reformatted? (or did the reformat effect a temporary "cure" ?
4 Have you the latest Windows Service Pack installed with all critical/important updates?
5 Any unusual entries in MSCONFIG (startup) or your Startup folder?
6 Have you reset your Router to its factory state ? (if not this would be a sensible step to consider, but make sure you have a note the settings you need before doing this)
7 Have you checked your Host file for entries other than local host?
8 Check to see if someone/something has slipped in a proxy server...check your proxy settings...anything there that you did not set up?
8 Does the problem occur when using Firefox or Internet Explorer or any other browser ?
9 To test your hardware to see if we can eliminate Windows or any software or drivers that you have installed as a potential source of the problem try booting from a Live distro of Linux ( Puppy Linux is good and its a relatively small download, only ---100Mb or so)
Give your machine a good workout, using Puppy, access the net (using an Ethernet cable to your router (not wireless) and see if the problem persists..... if it does then your hardware is a prime suspect.... if it doesn't and the problem no longer exists in Puppy then its pointing the finger at Windows, your other software or drivers.
Let us know how you get on.