WRT54G wireless mac address disappears, no wireless connection until reboot

Hi there,

After a while the mac address of the wireless part of my WRT54G (V1)
disappears (I can see that in the Status screen of the webinterface).
Wireless connection is also vanished until I reboot the router.

Then if I'm lucky the problem is gone for maybe a few hours, but most
of the time it is only for a few minutes or seconds. I see that the
router reboots just before it looses its wireless mac address.

Used all firmwares that exist (also third party to monitor syslog).
Used different clients.
Used different locations for the router.

All to no avail.

Any suggestions?

M.