i got a power mac g5 off ebay the other day. i worked fine

Hi,

It could be you need a new battery on the logic board.

Let's reset the hardware and try to get it squared away.

Do this:
To reset PRAM:

Turn off Mac

Find and hold down the following 4 keys at the same time:
OPTION
COMMAND
P
R
The command key is the Cloverleaf/Apple key.

Turn on the Mac while keeping the 4 keys held down.

Wait until the Mac chimes 3 times, release the keys and let the Mac boot normally.
Then....

To Reset Open FirmWare (PowerPCOnly)

Turn off the Mac

Find and hold down the following 4 keys:
OPTION
COMMAND
O
F
The command key is the Cloverleaf/Apple key.

Release the keys when you see the text screen

Type the following exactly, press return after each command:

reset-nvram (press return)
reset-all (press return)

The Mac will restart on its own.

Let e know if this helps. If not, then we'll move on to other tests.
Mike

Ok,

Here is what I would try in this order.

Turn off the display. Unplug from the Mac.

Turn it back on and let it go to sleep.

Connect it to the Mac. Turn on the Mac.

Does it come back on?

If not, then open the G5 side door and remove and replace the video card (after removing cable from rear of Mac). Then power up the Mac and Display again.

Does it work?

Let me know,
Mike