Panasonic Inverter NN-V673S microwave- shuts off...

Question

I have a Panasonic Inverter NN-V673S. The microwave worked for about 2
years. Now, the microwave runs for between 2-30 seconds (different
every time) on any setting i choose, then shuts off- e.g. I set it for
a minute, it works for 30 seconds, then lights turn off, yet fan keeps
humming, no heat produced and there is only a ":" on
the screen.Please tell me how i can fix this, preferably at home, as I don't want to pay for having it repaired. I olive in the UK, so finding a panasonic repairsman is difficult