If you are connecting to your router via a USB dongle then ensure that all your 'Root Hubs' in Device Manager are not set to 'allow the computer to send this port to sleep' (or words to that effect).
Unfortunately Windows 7 by default upon install sets them all to sleep mode.
System Manufacturer/Model Number Novatech (UK) iRush Pro OS MSDN Home Premium CPU Intel i5 Motherboard Intel DP55WB Memory 4Gb Graphics Card ATI Radeon HD 5770 Sound Card On Board Monitor(s) Displays Philips 170B
Keyboard Microsoft 3000 Wireless Mouse Microsoft 5000 Wireless BlueTrack PSU 750W Case Antec 300 Cooling Tricool Fans Hard Drives 1 x 1Tb
(7 Partitions) Internet Speed 6.1 Mbps
No, the router is connected by ethernet, not USB, but I just checked the Root Hubs as you mentioned anyway, in case they might be related to other non-router issues, and they are not set to go to sleep. Thanks.