Computer won't boot with a second GPU

[MatthewGB]

I'm building a mining rig with two GPUs (And hopefully 3 at some point), but the motherboard won't boot if two GPUs are in. If I put only either one in, it boots fine. My motherboard is from a XW4400 workstation, and has 4.5GB of DDR2 with a Q6600. It has 3 PCIE slots, an x16, an x4 with x16 size and an x1. I've tried using a riser in the x16, and using an x1 to x16 adapter in that slot. Everything works fine with one GPU, it POSTs and goes to OS. The GPUs I'm using are a GTX 980 and GTX 660. The correct PCIE power connectors have been plugged in, and a molex to the x1 to x16 adapter board when used.

 

[kaptainkuftic]

It won't boot all the way, but can you get into bios?

 

[dark_lord69]

You have 1 full speed slot and one that is 16x in size but 4x in bandwidth.
Even worse is the x16 slot adapter running at 1x bandwidth.

Direct Quote from HP:
1 PCI Express x16
1 PCI Express x16 (x4 bandwidth)
1 PCI Express x1

I realize this doesn't solve your issue but what I'm trying to say here is... I'm not certain your motherboard was designed to have 2 cards unless it's the ones specifically mentioned in the user manual...

PCI Express Graphics – Up to two of the following*
NVIDIA Quadro NVS 285 PCIe (128 MB)*
NVIDIA Quadro NVS 440 PCIe (256 MB)*
NVIDIA Quadro FX 560 PCIe (128 MB)
ATI FireGL V3300 PCIe (128 MB)
NVIDIA Quadro FX 1500 PCIe (256 MB)*
NVIDIA Quadro FX 3500 PCIe (256 MB)
ATI FireGL V7200 PCIe (256 MB)
NVIDIA Quadro FX 4500 PCIe (512 MB)

NOTE:
Two NVIDIA Quadro NVS 285 PCIe cards may be used together on any OS. Two NVIDIA Quadro FX 1500 PCIe cards may be used together on Windows XP 32-bit and x64. One NVIDIA Quadro NVS 440 PCIe and NVIDIA Quadro NVS 285 PCIe may be used together on Windows XP 32-bit.

 

[MatthewGB]

Resetting the CMOS fixed it, no idea why though...

@kaptainkuftic I meant it won't POST, and not even report any errors though it's speaker.

@dark_lord69 Yeah, although the manual compatibility list seems like BS. I was able to run a Q6600 which is not supported by the mobo, and now that I've fixed it it's running a GTX 980 and 660 simultaneously absolutely fine. Also, bandwidth makes no difference whatsoever for mining. Even for gaming you could get away with an x4 pretty easily, although an x1 would severly limit it.