Some time ago I had a Netgear RP614 wired router connected to the DSL modem,
and everything worked fine. Later, I had a Belkin Wireless G router
connected to the DSL modem, and everything worked fine. However, when I went
back to have the Netgear RP614 connected to the DSL modem, the same Netgear
wired router no longer worked with the DSL modem. Fortunately, the Belkin
wireless router still worked with the DSL modem.

Recently, I obtained an Airlink101 AR504 wired router. It worked very well
with the DSL modem. Surprisingly, when I replaced it with the Belkin
wireless router, the latter no longer worked with the DSL modem.

In other words, now I have a working Airlink101 wired router but a
non-working Netgear wired router and a non-working Belkin wirless router.
What did I do wrong?

Thanks for the help.