Roberts advice is sound. However, once relays begin to stick they tend to do so again and again and again. It's unwise to depend on something that has failed and fixed by banging on it.
The oven itself is good for scrap. There may be parts a tinkerer can use inside, but be forewarned, the microwave turns normal house voltage (120 volts) into high voltage (2000 volts DC)
Two things make the 2000 volts dangerous. First, it's high voltage. That alone should convince you that if you don't KNOW what you are doing then you shouldn't mess with it. The second thing, and here's where Robert is SPOT ON: That capacitor is storing 2000 volts DC RMS. What's RMS? Root Mean Squared. That means that 2000 volts AC can climb to 2800 volts DC when stored in the capacitor. Touch those leads with a screwdriver and you will burn the end of the screwdriver off. Touch them with your fingers and you can get an extremely painful burn and trip flying across the room. So Roberts advice is sound in that respect.
As for the rest of the oven; if it is still functional you can use it as a toaster / oven, but not likely very efficiently. It's best (if you can fix it or have it fixed) to call a professional. Otherwise the next best option is to replace it.
OK, I know that's not what you were asking. Piran and Jo Ann are both correct in the aspect that if the ceramic plate is used on a stove or cook top it WILL shatter, and somewhat explosively. I've messed with burning concrete many years ago (as a kid). Yes, these things DO send shrapnel everywhere - and painfully might I add.
You CAN use it in the oven, but why? So again, best advice may be to scrap the machine and replace it with new.
Hope this helped.
'')