Can't find right settings for Mageia 5 / Radeon R7 240

I just installed Mageia 5 from the full installer, and the install appeared to go fine, but now that it wants to reboot I get a "Sorry, but there has been a problem starting your graphical display" message.
Running drakx11 defaults to:
My actual hardware is:
Video Card: [AMD/ATI] Oland PRO [Radeon R7 240] (according to lspci)
Monitor: LG 29UM67-P (29" Ultrawide 2560x1080)
I've tried messing around with several of the settings, but all of them either just lock the screen with a non-blinking underline cursor in the corner, or give the following error:
I seem to be a bit over my head this close to the hardware side of things. I've run a few other distros (Ubuntu, Mint) but they just picked everything up during install, so I know it's at least possible.
Any help is appreciated!
Thanks,
Mike
Running drakx11 defaults to:
Graphic Card <ATI Radeon HD 6400 and later (radeon/fglrx)>
Monitor <Custom (Plug'n Play())>
Resolution <Automatic>
My actual hardware is:
Video Card: [AMD/ATI] Oland PRO [Radeon R7 240] (according to lspci)
Monitor: LG 29UM67-P (29" Ultrawide 2560x1080)
I've tried messing around with several of the settings, but all of them either just lock the screen with a non-blinking underline cursor in the corner, or give the following error:
An error occurred:
(EE)
(EE) Backtrace:
Try to change some parameters
I seem to be a bit over my head this close to the hardware side of things. I've run a few other distros (Ubuntu, Mint) but they just picked everything up during install, so I know it's at least possible.
Any help is appreciated!
Thanks,
Mike