SAPPHIRE HD 6870 - MOTHERBOARD NOT BOOTING WITH IT

[djolex]

Hi there!

I built a PC few days back, and it doesn't boot at all, the MoBo isn't turning on (fans not spinning), or it starts, stops, eventually booting.
I3-2100
SAPPHIRE HD 6870 1GB DDR5
CHIEFTEC CTG-500-80P
GIGABYTE P61-USB3
DDR3 4GB KINGSTON CL9 1333MHz
... the rest isn't important. When I put the 9800GT in, it starts every time, but when I put 6870, it doesn't start most of the time, sometimes it does, in 10 tries for an example.
What could be the problem besides the graphics? Because, when I booted it, i played COD4 in 250+ framerates on high... so I'm in a doubt what's the problem, if the GPU is working. EVERYTHING IS CONNECTED PERFECTLY, PSU with MOBO and front panel with mobo.
Please help

 

[djolex]

by the way, it didn't work on a 750w THERMALTAKE PSU, and for a miracle, 5 times in a row, booted from chieftec 500w with hd 6870...

then again, BAD LUCK, not working (

 

[ulillillia]

3 things come to mind:

1. You have a 2-rail power supply and you may have unintentionally put everything on one rail. The 6870 is a lot more power hungry than the 9800 GT. Put everything except the video card on one rail, the video card on the other.
2. There's a short or something causing the computer to turn off on its own to protect itself.
3. The video card is defective. Have you tried other PCI-express x16 slots?

 

[djolex]

I have 2x 6pin connector on the graphic, from the psu, i just connected that, i'm kind-a nubbish, so i don't understand the rail thing :/

i have only one slot