Am having the same problem with my v1 DG8234N.
Worked fine for ages, then I upgraded from 1.01.06 to a later version (this was about 9 months ago), then I experienced exactly the problem being described above.
I had a wired PS3, wired 360 wired original xbox and 2 wired PC's (some via a switch). Didn't matter which one was being used (could be just 360 could be all of them, could be one using the switch could be one wired directly)
3 or 4 times a day the wired connections would stop working but the wireless worked 100% fine, only way to get back was via a reboot.
Reverted back to 1.01.06 and the problem went away.
Last week we brought another 360 and having two going through the same router using UPnP meant that whichever one got turned on first had an open NAT and the other had a strict.
I read a review on
XBox Live The Guide : Help and advice plus Xbox games news, chat and more
where it said the DG834N didn't support two 360's with open NAT. Before I gave up, thought I'd see if there was any new firmware.
1.02.15 seems to be the newest so I gave that a go (doing it properly, resetting the router by holding the reset switch for 10 secs after the upgrade etc).
Excellent news, UPnP now seems to be working properly, both 360's have open NAT's.
BUT:
I did this Saturday evening.
3 times Sunday we lost the wired ports but the wireless was fine.
4 times today (Monday)
Driving me nuts. Do I get a new router, do I go back to the old firmware but not be able to use 2 360's on live properly or do I simply go mad instead???
edit: when it happens, cant log into router, its as though the 4 ports on the router have simply stopped (lights still on though). Son was on his 360 (wired directly) when it last happened, I then turned on my PC, dead for me too. Daughters screaming at us because she's having no problems on her wireless laptop and doesn't want to be thrown off yet again while we reboot it.