PowerMac G5 being a trouble child. Help?

Hello! I was recently given a PowerMac G5 under the circumstances that it was broken and needed some work.

Plugging the machine in was normal, the fans span up (not turbo jet mode like they do when it's kaput) the LED turned on and it made the start-up chime. However. No video.

I did all the standard stuff, reset the PRAM, reset the PMU. change the PRAM battery. and not much changed.

The machine did once spring into life in open firmware mode oddly, and a second time it came on with the question mark folder (as the hard drive is blank). but most of the time has no life at all.

Any ideas?

Thanks

Steve.