It may be just a fuse in the mains plug they do blow with old age,,,and there is a mains fuse inside the unit, plus others,, but there not normal type fuses so you wont have them, if its not the plug fuse blown then why has the fuse blown??? my gess is the microwave is faulty and this fault caused the fuse to blow,, first how old is this microwave???? and second
dont you try "having a go at fixing it" you could end up killing yourself,, even if the mains plug is out the wall,,,inside your microwave is a very big capacitor that holds lots of volts just like police stun gun's do
however this capacitor wont just stun you,,it will kill you,,so be warned if you tuch the wrong part and if you live to tell the tale,,all be it in grate pain from a hospital bed,, you may then ask yourself was it all worth it for a cheap fix??? so please play it safe
call in the repair guy or better still go out and buy a new unit and live to show it off to your friends,,
and im not trying to scare you,, im tell you as it is
warts and all,,, microwaves can bite you realy hard