I have resolved this problem at last.... :-)
I suspected that there was a problem with the power supply so I got in contact with Dream Multimedia. On sending them the serial number and a description of the problem they came back and said it was a known problem with the power supply. The psu in my box is an old design. Anyway they offered to replace the psu with a new version as an exchange for the old psu. All I had to pay was the postage.. Good result...
