Connection problem with cable modem

I have a problem with my internet connection. What usually happens when I turn on my PC (and my cable modem) is that the internet connection is ok for few minutes. Then it suddenly disconnects. It usually connects again by itself after some minutes and stays connected until I turn the PC off. When I was connecting to internet directly via university lan everything worked fine. Now I got a cable modem and the problems begun. When it is disconnected windows tells I have limited connectivity. It seems that the problem is that my PC and the cable modem aren't communicating properly, since I can't even enter the configuration page of the modem via web browser when I'm disconnected.


I found out that when I turn off both my pc and the cable modem at the end of the day and then turn them both on in the morning it always reconnects by itself after some minutes of being disconnected. But if have kept my modem on during the night, reconnecting might be much more difficult (may work after some booting). I have tried to connect with a laptop running XP professional at it works fine with cable and with wlan.


My PC has:
Motherboard: Asus M2N-E 2.0 with integrated network adapter
OS: Windows Vista Home Premium 64 bit (service pack 1)
Cable modem: Scientific Atlanta EPR2325 (connected to PC via ethernet cable)


Solutions tried:
Booting PC and cable modem XX times
Diagnose and repair function in Windows
ipconfig / release and renew
disabling TCP/IPv6
changing the ethernet cable


I just don't know what to do next. Does anyone have an idea how to fix this?

The only thing I can think of, as you've already tried a different Ethernet cable, is maybe it's a faulty modem. How long have you had it, is it still under warranty ?

I've had it for two months. But it can't be the modem since it worked fine when I used it with a laptop.