I have an old G4 quicksilver tower that has been a great work horse. it is now getting a tad old and has suddenly thrown up a good problem.

I was checking the cable into the back of the DVD drive when the machine booted itself on then turned itself off. since then it will onlt boot into the open firmwear window.
however it will not allow me to type "mac-boot" or anything else.
I have reset the switch on the mother board and also changed the PRAM battery.
after leaving it alone for a few days it did make it through to the desktop but froze up on me.

there is power coming through and the hard drive does start up.

any pointers would be great as apple do not support this slightly older machine.

thanks in advance