Burn at bottom of microwave

I would not risk it. Your better finding out why there is a burn mark there. The plastic film with the burn mark will be a specific one for microwave ovens. Basic peel and stick plastics could be the wrong type and it could also melt when the microwave gets hot.

Replace it. it may have a short near the plug causing it to melt. if the wires touch you may have a fire on your hands.

You can buy special chocolate fountain chocolate to use, or you can just use standard milk / dark chocolate chips and add 1/2 a cup of good vegetable or coconut oil for every pound (16 Oz) of chocolate.

There are many different variations on the recipe and you can Google CHOCOLATE FOUNTAIN RECIPE to get an idea of the many different options which include adding cream or liqueur.

Basically you just want to melt your chocolate on the stove in a double boiler if possible.
If you use a microwave, then carefully heat only on low power and stir after every minute.

Pour the melted chocolate into the fountain base and turn on the fountain for a few minutes. Then shut it off for a minute to allow it to vent any air and restart.

You can always add a little more oil to the recipe if the chocolate does not flow properly.

Good luck and enjoy.

If there is no indication of power present, check the main fuse.

THE ARCHING IS DUE TO EXPOSED METAL AND WILL BURN UP MAGNETRON IN MICROWAVE. TIME FOR NEW

Its no problem at all so long as it still runs normally. Only problem, is the smell will annoy you for a while. Give oven a good wipe down with a good cleaning agent.(I'm assuming the fire didn't get out of control).

Sounds like some metal is involved somehow. If the unit otherwise works, replace the damaged parts. Test with a cup filled with water.