Hmmm... Sounds like a program is running in the background that you may or may not know about.
You may want to running some good deep scans for viruses, malware and spyware. Which would be different programs pretty much for each. Also don't just rely on the standard Windows antivirus program. It doesn't do enough.
Should that not show anything, or not resolve the issue, I would then check as to what programs are running at the computers start/Windows start. Try going to "Start" and then in the search box type in "msconfig", without the quotes. Open that program from the list shown and go to the "Startup" tab. Check the list of running programs/files. Make sure that they are all files/programs that 'should' be loading. Careful what you enable/disable. Then go to the "Service" tab and check the "Hide all Microsoft services" box and then check the list of services still showing to make sure nothing is there that you don't want running, or automatically running.
Lastly, check the programs you do run/use and make sure none of them have anything set to auto access the net for something. Even browser add-ons, etc., can cause errors like that.