collegue has a Sony Viao running Mandriva 7.0. It suddenly decided not to
do wireless properly. What happens is that it can connect to the AP, gets
it IP address, but thereafter nothing comes in. If I do a tcpdump, if I
send out packets ( eg ping tcpdump shows the packets going out,
but nothing coming back in.
The fact that the wireless connects with the AP says that the wireless card
is working. What in the world could be happening that it does not allow
anything out? I switched off iptables ( service iptables stop) so it should
not be the firewall, and anyway tcpdump should still show returning packets
even if they are filtered.
Nothing in any of the /var/log logs that I can see.

route -n shows a default route and a specific route to the dns, but a ping
to the dns gives nothing back.

I need some hints as to what I could look for

He tried booting up a Kubuntu live CD, and it worked fine-- he could access
the net without difficulty. Ie, it does not seem to be a hardware problem.

Is there some /proc flag that could have been disabled but would still
allow the wireless to associate?