Router Keeps onn disconntecting computers.

I have a Motorola Surfboard Cable modem and a UsTec router. I use a laptop and a desktop and sometimes when I try to use both or am using some program which involves the internet, torrents, aim, etc- it gives me a limited or no connectivity message. I am then not able to do anything via the internet. I've tried connecting my computer directly to the cable modem and nothing is wrong there.... Any fixes? Thanks a lot.