A few of my 6 290 rigs will not post without a monitor, I'm not sure why. I bought a few displayport to vga adapters online for ~$5 each, and made dummy plugs from those. Each rig only needs one dummy plug, and it really only needs it to clear post, I got by with just one for a while, waiting for china mail. I got lucky and had a display port to dvi-d adapter from a v5900 I bought, worked fine as a test 
I just made a bunch and I leave one in each rig so I can remotely reboot them reliably.
You will not be able to dummy plug a 290/290x with a non-active dvi to VGA adapter. There are no analog outputs on a 290, so the non-active adapter does not work. You need an active adapter, usually has a big box built into it.
I just made a bunch and I leave one in each rig so I can remotely reboot them reliably.
You will not be able to dummy plug a 290/290x with a non-active dvi to VGA adapter. There are no analog outputs on a 290, so the non-active adapter does not work. You need an active adapter, usually has a big box built into it.