Imac G4 wont boot up

My son's G$ won't go beyond the grey apple screen (has a wheel/disc rotating?).

I saw an old thread that suggested pressing the Control (apple) key + option + p + r on start-up until it chimes (twice?) then let go. Unfortunately, the person asking for advice at that time didn't respond to say if it worked. Also, we don't know which is the 'option' key.

Can anyone kindly advise please?

sorry that should read G4.

It's between control and the Apple symbol.

Thanks Rob. On our keyboard that = Alt. We've tried holding Conrol + Alt + p + r and nothing happens (no chimes). So we tried Apple+Alt+p+r and it chimes about 5 seconds after but on releasing the keys it still sticks at the grey Apple screen. Also tried holding the keys to get a second chime (ignoring the first chime that happens on first switching on), that didn't work either. Any further ideas please?

Griffo said:

Thanks Rob. On our keyboard that = Alt. We've tried holding Conrol + Alt + p + r and nothing happens (no chimes). So we tried Apple+Alt+p+r and it chimes about 5 seconds after but on releasing the keys it still sticks at the grey Apple screen. Also tried holding the keys to get a second chime (ignoring the first chime that happens on first switching on), that didn't work either. Any further ideas please?

Click to expand...

It has been suggested that we try to boot from the Apple CD but cannot get the CD tray to open, as it requires a keystroke that only works when the system has booted - catch 22.

Can anyone suggest how we get round this please??

Griffo said:

It has been suggested that we try to boot from the Apple CD but cannot get the CD tray to open, as it requires a keystroke that only works when the system has booted - catch 22.

Can anyone suggest how we get round this please??

Click to expand...

Just pull open the white plate on the drive and use the emergency release (the little pinhole) on the face of the drive tray.

Thanks for the tip D3v1L80Y. In the meantime....

Had a call from my son saying that he left the mac on the grey screen for a long while, then came back to a black screen with, what looked like, a login requirement. He tried to type in his password but nothing appeared to happen.
However, he swiched off and back on again and, surprise, it booted up!

What concerns me now is, we don't know what caused the problem and we don't know how to run any diagnostics on a mac. Do they have anything built in or can one download stuff to try to find the cause?