Does the Radeon HD 4890 have the required 512 MB of VRAM? Does it support OpenGL 2.0? Are your display drivers up to date from AMD.com?
If you're not sure, choose Help - System Info, copy the data, and post it here.
By the way, note that it's NOT listed in the list of supported Radeon cards listed here:
From the above page:
Note: AMD/ATI 1000, 2000, 3000, 4000 series, nVidia GeForce 7000, 8000, 9000, 100, 200, 300 series and Intel HD Graphics (First generation) cards/GPUs are no longer being tested and are not officially supported in Photoshop CC and CC 2014. Some GL functionality is available for these cards, but it's possible that newer features don't work.
Thanks for the reply. It has 1gb of VRAM, but I'm not sure about the support for OpenGL 2.0. I believe it has support for OpenGL 3.0.