[G4] G4 in a coma

[Snoke Jay S NPRI]

Right after I got a brand new dual 1GHz, it had a similar anomaly.  In the end, two things caused the problem - the front power switch failed, and something on the logic board died.  the power switch was replaced, and I got it back;  it worked for about a day and then something on the logic board made them replace the entire logic board.

I hope the latter isn't your case.