* You can try to use the windows resource monitor under accessories and see if any other programs you have is suddenly using your network. This could also be other devices.
* Manually set the password on your router, and don't use WEP encryption if you are. (WPA is ok)
* Try using a cable to your comp in stead of wifi.
* If you have to be on wifi, check signal strength, try to improve it by moving antennas etc.. Scan for other networks around you, change to another channel than the one they are using etc..
But this could be 100 things. In the end, if nothing works, reinstall windows and c-rpg.