What you are describing sounds like you are using a passive display port adapter. Buy an active one (its $30 vs $15) and all should be fine. Active adapters have also been known to fail. Is this one the one you are using?
Be sure you are setting up eyefinity through catalyst, windows wont work. First step is to clone all monitors off the primary then tell catalyst where they are, then create an eyefinity group.
Lastly, a 7750 doesn't have the power to run extremely high definitions like the ones available to native 24" monitors. You will need more muscle for that. it'll run three monitors just fine, but when you try to do BF3 in 5760x1080 its gonna freeze up.
I'll order a new display adapter I guess, I'm currently trying to use...the
Star Tech DisplayPort to DVI Active Adapter -- DP2DVIS
I'm not doing 3 monitors for gaming...really its just to open more programs to work with doing my work day...I run a ton of websites and for social media I need lots of stuff open to view to save me time.
I've been running 2 monitors for 2 years no problem, I had no idea a bump to 3 was so "technical". I've been running ULTRAMON software for 2 monitors...does anyone know if Ultramon runs 3 monitors?
I use two Accell Active DP to DVI adapters ( on a 6950) from Amazon and they work fine. With AMD drivers pre-installed you really don't have to create an eyefinity display group if you are not going to play games across three monitors. It will auto detect and work without doing anything. http://www.amazon.com/Accell-B087B-006B-DisplayPort-Sin...
You only need the 13.4 AMD driver. If you have multiple drivers installed, Uninstall all of them completely including the Catalyst install manager. Then restart and make sure there is nothing left in the control panel ( AMD or Asus video drivers ), so that you only using the windows default driver. Then re-install the 13.4 driver. I understand your frustration with your Star-tech active adapter. I have seen other people having issues with those, don't why as they clearly are on the recommended list. I can only tell you that the Accell adapters seem to work for most people.
I just noticed that the Asus driver is much bigger than the AMD driver, so it can't be the same. I would uninstall all of the Asus specialty drivers, like GPU tweek ( if you installed it ), and install 13.4 first and then after you have everything working right, you could experiment with there GPU tweek driver, which is only an add on feature.
No, if your system runs fine with 2 monitors, then the third monitor is simply a function of the video card, driver and the active adapter. Possibly your Startech adapter is defective? Your gateway MB is probably an OEM from Asus, DFI or another major manufacturer.