A 2000 740 came with a MKII Nav computer.
Sounds like your MKII (if it's stock) has/is dying. Have you recently unplugged your battery? Did you wait for the red LED on the Nav computer to go out before unplugging your Nav? This can cause the nav to die.
One way to test is to try a known, working Nav computer in your car & see if that solves your problems.
2000 740iS. MKIV, 16x9, DDEs controlled by Euro fog light switch, reversed steptronic +/- pattern, paddle shifters, clear corners, Basslink, iPod video with stereo audio, TV tuner, gauge rings, ///M pedals, backup camera with 'on demand' switch, quad brake lights, Dinan engine & tranny software, windows/sunroof close via remote.
2003 540iS. MKIV, 16x9, PDC, CWP, TV tuner, backup camera with 'on demand' switch, paddle shifters, windows/sunroof close via remote, iPod video & audio.