S2400GP add-in video card not working

[idata]

Hi, I have Server Board S2400GP2 and I have problem with install add-in video card GIGABYTE GV-N550WF2-1GI (geforce GTX 550 Ti).

My server board:

updrade BIOS to SE5C600.86B.01.06.001,

BMC Firmware 1.16.4010,

ME Firmware 02.01.05.107

I installed one processor - Intel Xeon E5-2420 (to CPU1 Socket, CPU1 Power 8-pin is connected, CPU2 Socket and CPU2 Power 8-pin is empty)

I have 3 x DDR3 8GB RAM in blue DIMM slots for CPU1.

My power supply is OZC ZS 550W 135, 80 Plus Bronze

I get "Attention Document" with my server board box and they says: "SLOT 6, 5 and 4 require having two processors". But the "Technical Support"

(http://download.intel.com/support/motherboards/server/s2400gp/sb/g50295002_s2400gp_tps_r1_01.pdf http://download.intel.com/support/motherboards/server/s2400gp/sb/g50295002_s2400gp_tps_r1_01.pdf)

MAY 2012 says "SLOT 3, 4 and 5 work only when CPU2 is istalled", and SLOT 6 is for the CPU1.

When I install video card in SLOT 6 (and connect 6-pin power to card) - nothing happens. Even video card fan is off and card doesn't work.

When I install card in SLOT 3 - cards fan start with server board, but card is not working.

In both cases sever board boot from on-board video and in BIOS >ADVANCED>PCI CONFIGURATION>ONBOAD VIDEO option is ENABLED and DUAL MONITOR VIDEO is DISABLED, both options are inactive (I can't change them value).

LEGACY VGA SOCKET: CPU SOCKET 1

Is this video card (GTX 550 Ti) is compatible with this server board (S2400GP2)?

Or maybe video card require having two processors?

Or the power supply is too small for this configurationadd-?