The N64, like the SNES before it and the Gamecube after it, has a Nintendo A/V port. The standard configuration is a cable with composite video and audio RCA plugs on the other end. Unlike the SNES, you have to use an adapter to convert the A/V port to the RCA RF jack before you plug in the RF modulator (The SNES has an A/V port and a RCA jack for the RF adapter built-in). Turning on the deck is supposed to automatically switch Nintendo-branded modulators from antenna to line.
Check the memory expansion module as Nanoda indicated.
When a deck and games sit unused for a while, they get dirty, and you have to clean the edge connectors (cf. “blowing out the cartridge”). The male cartridge connector can be easily cleaned with a q-tip and alcohol, but cleaning the female deck connector will be harder. Nintendo made a cleaning kit that was basically a handle shaped like an N64 cartrigde with a piece of soft fiberboard in place of the male connector. You can also try repeateadly removing and inserting a cartridge, as this usually wears through enough dirt on the contacts to make a sufficient connection, but obviously this doesn’t actually get rid of said dirt and should be avoided
It’s supposed to boot instantly, but it may take a short time before a game starts up. Try turning the deck off and on or wiggling the cartridge in the slot if it still doesn’t do anything
Overall, unless your TV doesn’t have composite video jacks, you should go to your local game or toy store and get the A/V cable. It’s the same one used for the Gamecube. Also, if you have access to a known-good Gamecube, you can test the RF modulator and RF adapter on it.