BleepingComputer.com: Router Disconnects When Connecting 2nd Computer

I have a ZyXEL P-335U wireless router, which also has four normal LAN ports.
Currently I only use the normal LAN ports, and I have no wlan connections active.
The router is connected to the internet through an ethernet connection. (10/10Mbit)

Everything works great when I connect through the router with only one computer, but
if I plug in my 2nd computer, both connections will die after 10-60 minutes. All the lights
on the router keep blinking like usual, even after the connections die. It seems like some
outgoing traffic will still be possible after the connection crashes, but no incoming data.

I returned the router to have it fixed, but they found no problems and sent it back to me.

Hopefully someone here will have an idea of what could be the problem. Looking forward
to reading any ideas/comments/tips/help/whatever.

This post has been edited by joco: 22 March 2008 - 01:15 PM