Very odd router crashes - any thoughts?

[#1]

Every so often, my router locks up. Although all the lights say all is working fine, it's unreachable on either the wired or wireless networks, and there's no routed internet.
A hard restart and it comes back fine.
Sounds like a dodgy router, doesn't it.
So I replaced it.
And the replacement DOES EXACTLY THE SAME THING.
Any thoughts on what on earth could cause two separate routers to act like this?

[#2]

and the make of router is/are

[#3]

Is uPnP enabled?
I discovered (by trial and error) that both Windows XP and Windows 7 wireless connectivity failed after a few days with a Netgear 834Gv5 and could only be fixed by a soft (or hard reboot).
Disabling uPnP has cured this problem - with no apparent ill effects.
(It may call for some explicit port forwarding if you use certain software - especially interactive gaming).
The alternate fix is to use Linux - it continued to work flawlessly when Windows failed.

[#4]

Problem seems (fingers crossed) to have been a wireless ethernet bridge - the problems seems to have gone away since I turned it off. Lord knows what bad things it's doing, or how its doing them

[#5]

I know the speedtouch 585v7's that I use have problems with wireless and pnp combined.  Causes it to reboot.  You've not yet told us what model of router you're using.
-- gyre --

[#6]

I've used two.
A Belkin Wireless N, and a Linksys WAG160N. The former is slightly more stable in that I can usually still connect to it when I get a drop out although not to the internet until it's manually reconnected. The Linksys just dies and can't  be contacted although the SSID is still visible. In both cases the LEDs say all is fine, even though it's not.

[#7]

You don't mention if anybody in the house uses torrents, I found with some routers I had to reduce the number of half-open connections to under 50 in some cases to stop them hanging.