To confirm, if you set the microwave to run for 10 minutes with some water, does the timer count down, but the contents remain cold at the end of the 10 minutes?
I am confused the microwave oven must have power if the oven part still works, can you please clarify what you mean by the microwave doesnt have power (is it just when you set the microwave function that the screen goes blank)?
Right this sounds like a failure on either the control board or the function selector switch, and will need an engineer to come out to look at the appliance.
How old is the appliance, as this looks like a reasonably new model?
As the unit is out of warranty, its looking like you need to arrange for an engineer to come out and inspect the circuit board and function selector switch.
If you would like me to recommend a suitable engineer please provide your postcode.
Sorry for the delay in responding please contact AB Appliances on(###) ###-####1819
They charge around £65 to come to site and diagnose the fault, and provide cost for replacement parts.
Based on the first part of the postcode provided its showing within 10 mile radius, their postcode is BR3 4AB