R9 280x Extremely Slow On Boot & Operation

[rainbringer]

Hello,

first of all, I've ran through this checklist before posting this thread, but with no results.
Now, to the problem.
I've bought two identical PCs (lets call them 1st and 2nd) with the following build:

• Intel Core i5 4590 Tray
• Gigabyte GA-H97M-D3H
• SeaSonic 550W 80+ Gold S12G-550
• G.Skill F3-1600C9D-8GAB
• Sapphire Vapor-X R9 280x
• Corsair Force GS 128Gb SSD

(I've rechecked in 3 power consumption calcs and in voltage benchmark tests that 550w is enough for that build even during stresses).
On both PCs a clean install of Windows 8.1 x64 has been performed.
On both PCs the newest drivers for all parts are installed.

The problem is that 1st PC runs perfectly, and 2nd PC is extremely slow: POST is heard after 20-30 secs, screen refresh rate is actually visible (the refresh line is slowly moves downwards from screen's top) and games are absolutely unplayable.
Additional info:

• Both GPU cards runs great on 1st PC.
• Both of them runs horrible on 2nd PC.
• An old GPU (GeForce 9800 GT) runs fine on 2nd PC.

Actions I've taken so far:

• Measured the voltage of 2nd PC's PSU - 12v rail provides 12v +/- 0.1V on both 8-pins connectors.
• Verified in AIDAx64 that the voltage graphs are stable.
• Verified that all the parts are sitting well in their slots on motherboard and all the power connectors are connected well.
• Restored defaults in the BIOS.

Any ideas how can I identify the problem? The problematic part?
I'm almost desperate!

Thanks!

 

[Big B]

While you could do a part for part swap of anything on the motherboard, there's not much to look into. The drives shouldn't have an impact, so you're left with the CPU or RAM. The CPU would be the more likely culprit, due to some PCIe lanes coming off it, but even so, the 2nd motherboard doesn't like the 280X's. So, we're looking at a BIOS update or an exchange. See if the BIOS on each is the same version, and if not, update the 2nd system to match the 1st. If it doesn't work, then I would exchange that motherboard.

 

[rainbringer]

The BIOSs of the two systems are exactly the same version.
What did you mean in "exchanging BIOS"?

Update:
after a full power discharge (disconnecting the power cord and pressing ON button for 5 secs., and doing so 3 times) - the systems boots and works fine.
The problem repeats after a night in shut-down mode.

Update:
As proposed in some threads, I've changed PCI-E configuration in BIOS to Gen2, instead of Auto/Gen3.
Apparently, that solved the problem - the 2nd PC runs and boots fine for two days in a row.

The question is: what is the cost? What is the downgrade in GPU's performance, when the slot is configured to Gen 2 ?

 

[Big B]

If a BIOS update for the problem, I was suggesting an exchange, but if the BIOS configuration helped, that's good. The latest PCIe standard is at PCIe 3.0, and the main focus is higher bandwidth than PCIe 2.0, which was faster than PCIe 1.1/1.0. Unless you saturate the PCIe lanes with your current cards, the current setting won't make a difference if you're not maxing it out. Quad cross fire might do that, but you'd need 2 cards sporting 2 Radeon 280's, but people looking for that overhead tend to look at LGA2011 boards with tons of PCIe lanes and quad-GPU capabilities---beyond what you're doing here. Basically, it shouldn't have an effect at all.