No signal at monitor from G5 quad?

[UlsterApple]

Hi folks - I posted this problem as part of a number of problems under the PowerPC section but if it's alright I'll raise the profile of one of the elements in this section?
I bought a refurbished quad-core G5 from eBay two weeks ago; on arrival none of my older monitors would fit the factory-fitted PCI-E graphics card (it's DVI while my Studio display is ADC and my LCD monitor is VGA) so I used an adaptor from the VGA monitor lead to the DVI socket but received no signal at the monitor. I thought maybe it was the fault of the adaptor so I then purchased another monitor with DVI connections but this also gets no signal from the G5 - only the message "no input signal is being received".
I've checked the graphics card is properly seated and that nothing internal has been dislodged in transit. Anything else I should look for, or any tests I can run?
If I require another graphics card eventually what should I go for?

 

[UlsterApple]

Problem over - solved by accident and caused by my error in the first place!
I noticed the white LED on front was flashing, and realised it may be a code sequence as in my Studio display. Sure enough it was telling me ' no memory is installed' and I remembered I had already installed 2 GB of new memory before first startup. I installed it in pairs, as it said, but just not in the right sequence of slots. Once I reseated the memory - correctly - the G5 ran perfectly.
SO: NOT the graphics card as suspected, but my over-enthusiasm at getting a more modern Apple. DOH!