Is there a GFCI on the cord? If so, even if it lights up it might not be sending power to the spa.
(If there is no GFCI I hope it's plugging into one or the breaker for the circuit is GFCI, Don't use the spa if there isn't one))
It's possible it's just a bad GFCI.
If not you need to pull out the control box and troubleshoot further.