Radeon hd 4870x2 won't let computer turn on

[ajn]

I got this card from my mate and with his computer, it all worked fine. we have the same setup (cpu,mb,ram etc) except he sold me the radeon hd 4870x2 and 750w psu, so I basically "got" his pc now. But there have been issues I couldn't figure out so I thought I might have some help here.

1. I've plugged the card in to the pci-e16x slot, connected the 6-pin cable to the 6-pin slot(intgr with the psu), and connected the 8 pin(6+2) cable to the 8 pin slot(a separate power cable). After doing this I try to turn the pc on ---> nothing happens! I read that the lights on the edge of the card blink(for some sort of self test) and they'll do it but nothing actually starts running, not fans, not the hardrive, not the psu, none. The red leds on the card only flash quickly so they won't stay.

2. If I leave the 6 pin slot from the card unplugged and connect the 6 pin power connector to the card's 8 pin slot (the one that is intgr with the psu, leaving the 8pin, 6+2 cable unplugged), the machine will start but loads a text on the screen that says 'power connectors have not been plugged properly' etc etc. but then there lights up the 2 last red leds (which should refer to 6/8pin powers unplugged) so I assume that the 8pin cable or psu's 8pin slot is broken, what do you think?

or 3. I have not connected the power connectors properly but there is only one way to plug them so I highly doubt this.

thanks for any sort of help!!

 

[shin0bi272]

are the 6 and 6+2 connectors native to the psu or are they attached to a 4pin molex?

 

[ajn]

are the 6 and 6+2 connectors native to the psu or are they attached to a 4pin molex?

native. only 1 little thing I noticed was on the 8pin cable, that the 6+2 head where the additional 2 pins gets their power from have a shared line. in otherwords, if 1 pin is connected to the psu, the power is led to those 2 slots. meaning like this:

[] []
\ /
\/
l
l
[]
just thinking that the card, regarding to this, still won't get enough power? one of our friends, who works on a pc field, disassembled these parts from my buddy's computer, he might have confound with some cables similar to this and promised to deliver me a secondary cable that doesn't have this kind of shared powerlines.