回複：我新安裝的ROUTER出了怪問題，請教！

If you use MOTOROLA SB5000, see if all 4 lights are on. That should tell you if your cable modem or your Comcast is working or not.
I have almost same setup are yours except with a Linksys Router. Try to connect one of your computer directly to the modem for 2, 3 days and see if disconnection happens again.If not, it could be your router.