Motherboard not posting after upgrades

[Kraynor]

Old system specs:

Asus P5KC
Point of View 500W PSU
8600 GTS
8GB OCZ RAM
2x 500GB WD Caviar
1x 150GB WD Raptor
LG DVD-RW


After upgrading the graphics card to a 4870X2, and the PSU to a Corsair HX1000, the system refuses to post. Connected up my old PSU to the 4870X2 and motherboard and it posted, and even ran properly until the graphics card tried to pull more power which resulted in a system shutdown.

RMAd the PSU and they sent it back saying it was working perfectly (2 days running Sandra's Burn-in with a Q9300 and 2 9800GTXs). Hooked everything up again, same problem.

Put back in all my old parts and the system ran happily for the 2 weeks it took for the RMA to be processed and returned so... frankly I'm stumped.

 

[merlinbadman]

Have you tried the new PSU with your old graphics card in? That will help narrow down the problem.

Does your old 8600GT use an additional power source?

What additional power does the 4870X2 require? 2 x PCI-e 6-pin?

 

[kubes]

When you say the PC refuses to post, do you mean nothing comes on? Or do fans and stuff at least turn on?

 

[Kraynor]

Ah sorry should have been more specific.

Tried the new PSU with my old graphics card, and it didn't post.

What happens with my old graphics card: all my fans and LEDs turn on briefy then the system turns off and restarts.

What happens with my new one: Everything turns on and stays on without posting, it just sits there idle for about a minute, then turns off and restarts.

The 4870X2 takes a 6-pin and 8-pin PCI-e connector (yes, I'm sure I have the right ones connected). The 8600 GTS takes 1 6-pin PCI-e.

I managed to get the system working with my old PSU and the 4870X2, but it crashed once I tried to do anything that pushed the card any bit. Looked it up and worked out it's a 'not enough power' crash.

Did some more research and found out that other Asus P5 users have had problems with the HX1000, so going to look into picking up a Gigabyte board. I was looking for an excuse to upgrade anyway...