oh dear - I had one that decided to mess up after an ota with bad boots and freezing touch screen. that took about ten wipes and factory resets to get it going again.
 
have you asked advent or pc world about it? if as usual they deny all knowledge and you'ld have nothing to lose then I'd crack the case open and check the battery charge level as that might be the reason it wont come back on if it got too low trying to boot up. if its below 3 volts then you might need to just start it by patching the red and black wires from a normal usb cable to the battery ones.
 
unfortunately the advent needs a different technique to the standard power and vol + technique. managed to root my faulty one to work as per the youtube vid I used as a guide but to be honest I'm not sure exactly how. 
 
the advent instructions require you to install a set of drivers to your PC then boot it up with a key combination. as the usb port was not responding I tried the sd card rom install instead.
 
I'm no expert but be patient with it.
 
I assume you aren't in the UK or I'd say post it to me and I can have a go.