black screen, won't boot, won't charge

Please help. I've had my 3GS for a few months and it appears to have died. It won't charge from the wall charger or from my mac (I've tried two different cables) plugged in directly into the mac followed all the usual suggestions (press and hold both buttons until my hands hurt and still nothing, no sign of liquid damage, itunes won't recognise it)

I'm stuck. I've been having the random shut down problems and I've recently taken the phone abroad (mainland Europe) where it charged fine ut the battery ran down quickly.

Please help.