Call your dealer, a service man, or get a volt meter. Start with the supply voltage, ck the supply to the tub, should be a GFCI. Push the test button, if it trips, then voltage is present at that point, then check the voltage at the tub. Chances are, your are going to need service considering what little info you have.
What kind of Hot Tub is it, 220v or 110v, ANYTHING on the display, back lighting?, any sounds or clicking, indicates something is getting electric and trying to work? OR, is it just DEAD?