Only two screens can be active at the same time

I'm having the problem that only 2 monitors seem to work simultaneously. Right now I have these monitors:

• Samsung SyncMaster S24B350 (VGA to DVI adapter)
• Samsung SyncMaster P2450H (DVI to DVI)
• Iiyama E2483HS (HDMI to DP cable)

and this setup:

• Sapphire R9 270X
• Windows 8.1
• Latest drivers (according to AMD driver autodetect)

The Iiyama one is the one I'm trying to add to the setup. However it only works when I remove another screen.

When I look at my config this is the view I get (the not detected display is the onboard VGA adapter):

When I try to change it to 'extend desktop to this display', I get the "The display settings could not be saved. Please try a different combination of display settings." message.

In my search for an answer I have come across the statement that I need an active HDMI to DP adapter.

This is the cable I have:

Am I correct in assuming this is a passive one and that this is where the issue is located?

If not: what suggestions do you have to fix this?

To use more than 2 screens on an AMD card, at least one screen must use a (true) DisplayPort connection. Your cable is indeed a passive adapter (utilizing the HDMI fallback mode on DP+). As such, this is not a true DisplayPort connection.

Active adapters (or "converters") are usually advertised as such. Unfortunately, there are quite some low-quality products on the market that may not work. I suggest to go by Amazon ratings to improve your chances of finding a good one. This one looks decent enough.

Also, take note of the different plug sizes. Due to Apple's use of Mini-DisplayPort, these are the most common adapters.