The DisplayPort of the GA-A75-UD4H(rev. 1.0) motherboard is not working properly with a newly purchased HP Elite L2201x Displayport-only monitor.  The new monitor is displayport only.  

There is signal, and occasionally the monitor shows a black-and-white display at 640x480, but will not display anything else (including BIOS bootup screens - it is blank.)  So I can run the system with dual monitors, extend the desktop to the DP monitor and it's a greyscale at 640x480. 

Both the monitor and DP cable will work on other computers (I'm using it now). The VGA and DVI of this motherboard also work correctly.  Even if I reboot the system and use the HP Elite L2201x by itself (no other monitors connected) I don't see a picture.

Gigabyte was not helpful, and offered to replace the motherboard.  But before I send the board away for three weeks and take the working system out of commission - what's the chance it's the APU that's at fault?

I just built the system - everything is new and uses default (automatic) settings in the BIOS.  There is no overclocking.  Except for the displayport issue, the system works flawlessly.

XP - SP3, 32bit, new system

Thermaltake TR2 W0070 430W ATX12V v2.3 Power Supply

G.SKILL Sniper 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-8GBSR

AMD A6-3650 Llano 2.6GHz Socket FM1 100W Quad-Core Desktop APU (CPU + GPU) with DirectX 11 Graphic AMD Radeon HD

GIGABYTE GA-A75-UD4H FM1 AMD A75 (Hudson D3) SATA 6Gb/s USB 3.0 HDMI ATX AMD Motherboard, Rev. 1, upgraded to V7 motherboard Bios

NZXT Source 210 Elite White Steel with painted interior ATX Mid Tower Computer Case w/ Black Front Trim

SSD hard drive

[CRICKETS]

Can anybody help?

You answered your own question. Gigabyte has already offered to replace the board. Which is all you can do. You won't know if its the display outs or the APU. I wouldn't place blame on the APU because its sending out a video signal. If it were not I'd blame the APU. This point all you can do is test each one to see what the issue is.

Because regardless of driver settings you should always be getting post screens of some sort.

I5 3570K@4~5.0ghz: Gigabyte GA-Z77X-UD3H:Corsair Hydro H70w/Delta 240CFM Fan: 16GB Corsair Vengeance DDR-3 1600: 2 XFX Radeon 7950 @ 1150/1575 : Corsair AX 860 PSU: x2 WD Black 1TB HDD's: 90GB OCZ Agility 3:CL X-FI:Corsair 500R Arctic White Edition:3 22inch Asus monitors Eyefinity @ 5294x 1050(bezel comp) : Alienware Tact-X Keyboard: Naga Razer gaming mouse:Corsair Vengance 1500 Headset .