S66 / S65 help

[ianoble]

Hi - i have an S66 which was locked to Cingular in the US (i am in the UK).
I fully charged battery and successfully unlocked the phone. I put an orange sim card in the phone and everything was fine.
I then unplugged USB cable and phone turned off and refused to turn on again. Screen flashes white for a fraction of a second but that is all. Very occasionally it will work OK for 5 minutes or so then switch off again (though 95% of the time it just won't switch on).
However it will happily switch on and works perfectly if it is plugged into a charger or a USB cable.
I take it that this is a hardware fault rather than anytrhing that could be cured by flashing - am i correct?
Many thanks for any help or advice you can give me.
Best wishes - Ian

P.S - it does the same with 3 different fully charged batteries which work fine in my SP65 so obviously not a battery problem