Well let's see, the first problem to check is whether or not your NES's RF adapter port works. My NES's didn't, so I had hook mine up via the A/V ports(the yellow and white plugs, red is unused because the NES has mono sound).
A second thing to check may be a crappy RF adapter. Mine was about 15 years old and refused to let many video signals through.
And last, please tell me you tried this first, but most NESs have cartridge response problems by 2002, so check that, if somehow you DIDN'T check that already.