odd start procedure on MB G4 17"?

Hi

Have a 17" PB G4 mod A1052, 1.33ghz. Os 10.5.8, 750 mb ram 80gb hdd, battery ok.

The problem is that if only pressing the power-btn the hdd, dvd and chime appears, but after a few secs it shuts down.

To be able to start I need to hold the cmd-buttan untill the grey screan appears.

Once past that it works properly....

Have done all resetting, nothing corrects the error.