There may be a reset switch you could try pressing on the unit. Not much more to do unless you have some diagnostic tools and knowledge. A close visual check might turn up something. For example, one year, I had a mouse electrocute itself across my main a/c contactor sometime during the winter. When I tried to turn the a/c on in the spring, nothing...the fluids had gummed up the contactor and it was frozen solid. Some liberal use of contact cleaner, and all's well again without a service call.