No Power to the Hot Tub?
Check the power and circuit breaker. Flip the breaker's off one at a time, if your breaker panel is not labled accordingly. If the hot tub does not power up, it may be a fuse.
Check the fuse if the GFCI (Ground Fault Circuit Interrupter) does not stay set. If the fuse is blown, replace it. If the fuse continues to blow, it may be an indicator of an internal wiring problem.
Examine the heater element if the GFCI keeps tripping. Look for corrosion, burns and pinholes. A heater element that's damaged will short out due to water intrusion, causing the GFCI to trip. Should this be the problem, the heater element will need to be replaced.