Rig wont start with multiple Gpu's

[BTCsovjet]

Hi.

I have just build my first rig and ran in to some problems.

First I tried it out with just 1 GPU and everything worked fine.
But when I add another or 3 more GPUs the rig will start up, all the fans on all the GPUs will work fine but I cant get any signal to my monitor.
Tried the MBs HDMI and all the GPUs HDMI and still nothing.

What is causing this?

Its 4x Gigabyte R9 280X on a Gigabyte z87x-ud3h mobo.

Anyone?

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[prowler9]

Try adding them one at a time, ive had this when i was building my rig last week, also get remote desktop so u dont have to rely on the monitor