[ltp] Wireless failing to connect

[Phil]

After many months happily running Ubuntu Feisty my T60 has suddenly 
started misbehaving.
Connecting to my home wireless network has become really painful, but 
connecting to my office wifi is no problem. Before this started 
happening I'd work, s2ram, go home, wake up and it would connect fine. 
Then I'd sleep it again, go to work, wake up and again, no problem 
connecting.
Now, when I go home, the nm-applet shows my home wifi and tries to 
connect but fails after 30 secs or so. I can get it to connect by 
rebooting - most times - although somethimes it takes more than 1 boot, 
sometimes I have to disable and re-enable wifi.
No problem connecting to work.
Both networks are encrypted, but I also have an open wifi at home (which 
also fails to connect).
I've no idea why it's suddenly gone bad after many months of OK 
behaviour. I've installed all updates - but never noticed a wifi update.
$ uname -a
Linux phil-t60-linux 2.6.20-16-generic #2 SMP Sun Sep 23 19:50:39 UTC 
2007 i686 GNU/Linux
$lspci
...
03:00.0 Network controller: Intel Corporation PRO/Wireless 3945ABG 
Network Connection (rev 02)
...

Nothing in the system log other than repeated "ipw3945: Detected 
geography ABG (13 802.11bg channels, 23 802.11a channels)" messages. 
When wifi works there's only one of these, but when it's not working it 
repeats every few seconds.

Please tell me where to start diagnosing this problem,

Thanks
Phil