Good day,
I have a weird problem with motherboard likely, i'll explain the details below:

Description:
PCI-e slot appears to not be working right. My graphics card in that slot stopped working, and once in a blue moon it starts to work again.

History:
It happened during a forced shutdown of a PC during some 3d rendering (in a video game). As I turned it on, the graphics card in PCI-e slot did not work, so I had to switch to an in-built one (which works fine).

Occasionally the in-built card stops working after a restart, and when I switch the monitor to a PCI-e card it works. But it happens so rarely it's hard to recreate.
If I could leave the PC working while the PCI-e slot is working, i'd certainly do so, but it's not the case.

I tried 3 graphics cards of various producers (that worked fine on other PCs), and they also have the same problem on my home PC. That makes me think that the problem is with motherboard, and not with graphics cards.

The fans on the cards I place in PCI-e slot are working, so there should be power. Device manager refuses to recognize the graphics cards other than than the in-build one.

My system is Windows XP Media Center Edition with SP 2
Edit: PC is gateway GT5056
Processor AMD Athlon dual 64 (x2)

May be there's a way to enable the device inserted in PCI-e slot through BIOS?
Hope this BIOS info will sound helpful if you would like to give an advice on my problem (I don't anything in BIOS, messing with it without knowledge is rather risky, as I thought).

Code:
Key Name: HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System
Class Name: <NO CLASS>
Last Write Time: 14.03.2009 - 17:49
Value 0
Name: Component Information
Type: REG_BINARY
Data:
00000000 00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................

Value 1
Name: Identifier
Type: REG_SZ
Data: AT/AT COMPATIBLE

Value 2
Name: Configuration Data
Type: REG_FULL_RESOURCE_DESCRIPTOR
Data:
Interface Type: Invalid
Bus Number: -1
Version: 0
Revision: 0
Partial Descriptor 0
Resource: Device Specific
Disposition: Undetermined
Reserved1: 0x00000000
Reserved2: 0x00000000
Data:
00000000 80 00 fe 03 00 00 3f 00 - fe 00 01 00 ..þ...?.þ...

Value 3
Name: SystemBiosDate
Type: REG_SZ
Data: 02/10/06

Value 4
Name: SystemBiosVersion
Type: REG_MULTI_SZ
Data: Nvidia - 42302e31
)Phoenix - Award WorkstationBIOS v6.00PG
oC(Phoenix - Award WorkstationBIOS v6.00PG

Value 5
Name: VideoBiosDate
Type: REG_SZ
Data: 10/19/05

Value 6
Name: VideoBiosVersion
Type: REG_MULTI_SZ
Data: Version 5.51.22.30170
Version 5.51.22.30170
Version 5.51.22.30170

ward WorkstationBIOS v6.00PG