No display from PC with graphics card or onboard graphics

Depends on whether its because of how much power the card is drawing, some power comes threw the board still even with external 6/8 pin gpus.

I had a motherboard that ran fine with my 980 in it, till after some time in a demanding application would blue screen.

So I've tested the PSU. All seems OK with the voltage, though I have yet to find a way to test the current draw...
I was also unable to test the output from the PCI leads. Does anyone know any way of doing so?

I've also spoken to a few mates, and the only person who has a good enough PSU and comparable graphics card to test on is my Ex... Needles to say that won't be happening anytime soon haha

The local PC repair shop refuses to test my graphics card without the entire system. Which is fairly moronic and infuriating. I don't exactly want to had over my system with all of my data sitting there.

Well then... It would seem that one of the connections from a MOSFET on the GTX 770 has... removed itself? It appears to have been cut clean off, with no evidence of physical trauma.
I've re-soldered it and reverted back to the stock cooler. All seems to be well now.
Still, I've bough a new card and sold the 770 to a friend (with my own 'moder's warranty').
Also happened to melt one of the PSU cables whilst using this worthless PSU tester (why were these even conceived? I can check the voltage in the BIOS when I boot up with the 9800GT), so I've had to repair and re-sleeve the cable with some awesome new braid.
So I now have a slightly better system with fairly minor costs :D

To correct Phyrce, the PSU can supply 45A on the 12V rail. But I should have looked into that myself as it is my PSU haha Info online can be inaccurate sometimes but I appreciate the effort :)

Anyway, cheers guys for the suggestions and the effort (Y) Much appreciated