Weird Problem

I apologise in advance to the good people of this list because this may not
be a driver problem; but I don't know where else to turn to help me
troubleshoot and solve this problem.

I have just lost my Internet connection in Linux for no apparent reason.

I have been using the system with no problems for months now - it is my
primary home PC and I almost never boot into Windows any more. Yesterday I
upgraded my kernel (via RedHat's up2date system) from 2.6.6.something to
2.6.7.something. As usual I had to re-make the at76c503 drivers but that
worked just fine. I have been using it ever since with no problem. This
morning I was surfing to make an online flight booking and found that the
site I needed would only work with IE5+ (urghh!) so I switched to Windows
(dual boot system). I made the booking and then switched back to Linux.
No Internet!....

If I do a modprobe the at75c503 driver seems to be loaded OK and dmesg seems
to confirm this.
BUT... iwconfig says no wlan0 device (or some such).

It is clearly not a hardware or ISP problem because I am writing this to you
the same system (now back in Windows unfortunately).

What happened? Why working one minute and not the next - I made no changes
(that I am aware of)? The only thing I did that was different to usual was
that I did not take care to close every open application before I shut down
(using the normal "log out -> shutdown" method) and I did have several open
applications including a running clamscan virus scan going in a terminal. Is
it possible that a file has become corrupted somewhere?

I did try unistalling and reinstalling the driver - no joy. I also tried
booting back in the 2.6.6 kernel with a similar lack of success.

How do I troubleshoot?

I hope you can help.

Many thanks - as always

Mark