Hi!
If it's not connected to anything and it still does it's little dance it's pretty much internal.
Although it could be a bad power cable. Have you tried moving the power cable a bit? IF you jerk it and it cuts the power it might well be the caus. Aside from that I cant' think of anything.

What are the signs of the power interruption? Are any lights or LCD display black out for a split second? Any flickering?

At this point you might want to take it to a repair shop. Whatever causes this nonsense isn't worth trying to figure out by yourself. An experienced technitian can fix her up. You're suppose to enjoy using it not drive yourself crazy.

Try the cable thing, but something tells me it's not the reason. Internal battery might well be it but I can't say for sure.

Okay, good luck dude. Hope it works out.

-ED-