Do the gauges come alive when you put the key on? If so, you could have more thank one issue. The beepers go bad in these. If gauges are working when key is on, I would troubleshoot/replace beeper and test starter solenoid. All this assuming that brand new battery is good and fully charged.
1) please verify that battery cables are connected to the proper battery posts...yes people have inadvertantly switched them.
2) NO KEY...press SS button...does the ski wake up? message on the guage? If no, then you don't have battery power to the MPEM. Trace RED battery cable to electric box, open box, check 15 amp fuse....if bad - replace, if good keep tracing wire (probably Red/purple) to mpem....check fuses on the mpem (should have 5 and 15 amp fuses there)...test all wiring for continuity as well.
3) SS switch could also be bad, beeper is bad, DESS post could be bad
4) report back with findings and we will continue with suggestions....