While working at the computer today, I noticed that the APRS map was empty. Checking the raw data at www.aprs.fi I found that M1ABD had not beaconed for over and hour and was, therefore, probably off the air. When I went to get the keys to the site I found that contractors had been working at the site today. On arrival at the site, I found the power was on and all the electrical equipment was working, except for the computer which was turned off. I re-started the computer and M1ABD burst into life again. I am not sure what the problem was, but it all appears to be working normally again.