Network problems after reboot

Hi,

I've got a server which preforms NAT and runs a webserver. I've got it
working for about 46 days, but them my little brother reset my server and
now it doesn't work anymore. Here's the problem, the network seems to
function fine but after about 10 mins from the client computer boot up the
netwerk between the server and that client goes down. I've i ping the server
from the server it complains about no route to host under linux and just
times out on windows.... I've i ping from the server to my client the
network goes up again ! I've got a dualboot on my pc with linux (RH 9) and
win98, both have the same problem. The server runs RH9 to with kernel 2.4.20
and iptables (which is configured as a firewall and for nat)

Anyone knows what the prob might be?

Many Thanks In Advance,

Robert Mens
(E-Mail Removed)1