Doesw it blow the internal fuse or trip the house breaker after that?

Well your model number doesn't come up but If it's an inverter model thats where your problem could lie is a bad invertor

Sounds like the magnetron is leaking RF. The mag tube comes on 3 seconds after you hit start, that RF hits the board causing it to go blank and then come back on. To test this, you can drop the control panel down and try to heat up some water. If the oven cooks longer than 3 seconds the magnetron needs to be replaced.

To verify the mag is leaking you really need a leak detector, but you can just replace the mag and find out if that is what is causing it.Mags run anywhere from 70-130 you can find generic mags for less you can basically put any mag into any microwave as long as it mounts.I mentioned the invertor because Panasonics its either the invertor or the mag. The invertor is a circuit board that replaces all the hi voltage on a microwave the cap diode hi voltage transformer etc. 1 board does all that. Generally speaking a mag carries a 5 year warranty but the labor isnt covered and manufacturers wont ship a mag to the customer because of the risk of elec shock. Microwaves usually aren't worth fixing when they go down because you can by them so cheap anymore unless it's a convection or speed cooker like the Advantium. If you spent under 200 for it it's gonna cost more than half that to fix it If a person can fix an appliance for half or less than half of what it cost new it warrants fixing them.