Could be your router/access point, of course nobody knows for sure as you haven't told us anything about it (ie. make/model/firmware revision, a/b/g/n?).

There's not much point discussing wireless problems unless we have all the specs and information about both parties involved - your N800 and the Access Point. If you've got an Access Point that is well known as "good" (eg. Linksys WRT54GS) then we can eliminate it as a likely problem.

Try upgrading your Access Point firmware to the latest available if you aren't running it already.

Try disabling Power Save Mode on your N800 wireless connection.

Check you or someone else hasn't enabled the seriously overrated MAC filter in the AP.