Advent 7104 wont start up

Hi

Ive had this before but cant remember how to fix it. I left my Advent 7104 on and when I came back to it, it had shut itself down. On pressing the power on button nothing happens except the red power light flashes 3 times.

Ive tried the usual, disconnecting the battery and/or power supply but nothing helps. Any ideas?
Thanks

 

have you tried running on mains without the battery

 

yeah, still the same