upgrade Netgear MR814 -> WGR614 or WRT54G routers: no internet

Older "B" worked well but "B/G" does not see internet.
Same results with both routers under W2K and RH9.

4yr-old Aptiva desktop: both W2K and RH9 with MDK-kernal failed with
both new routers.

Thinkpad-T20 with both W2K and Debian3.1 or Mdk10 failed with WRT54G,
(did not try WGR614 yet).

I suspect Optimum-Online cable provider is the problem since: 2 PCS, and
two OS's each.

Has anyone encountered such problem?

Problem solved by using old MAC address from old router.