Connection transmitting at max speed unauthorized

The last two days my internet connection has started transmitting / uploading to internet at max speed, this slows connection down completely but i cant find what is causing this, it happens a few seconds after connection to internet. Today my pc crashed and restarted itself then when i went online again the uploading began, the previous night it happened around the same time at 10pm gmt and remained like this until i switched it off around 12pm.

i have scanned with AVG Anti-Spyware, PC-Cillin Anti-Virus but they came up with nothing. Before the problem i had just windows firewall running, now i have ZoneLabs too. I also tried system restore with no luck. :cry

My connection is 8mb broadband with around 300kbs upload speed.

Thanks for any advice