I’m using Windows 7 Ultimate x64 and have an ATI Radeon R5450 Graphics Card… I’m using Blender 2.78c x86 since I always get a startup error with blender 2.78c x64, but my problem is how to use the GPU Compute with Cedar my CPU lags for at least half a minute then Blender crashes when I try to render the default box in Blender Cycles… I also tried opening blender in CMD set Cycles_OpenCL_Test=All but it still doesn’t work. I saw my GPU already listed as compatible with blender, but it still does not run.
That card is 7 years old, comes with just 1 GB of VRAM and is only passively cooled.
Even if you could get it to run, I’d wager the performance will be abysmal…
2 GB VRAM are more or less the bare minimum for GPU rendering these days.
BTW, not sure where you got from that your card is compatible. AFAIK Cycles OpenCL only supports graphics cards with GCN architecture 2.0 and above: From my understanding that requires at least a Radeon HD7xxx card…
Not quite sure wether you are asking for how to activate the GPU computing or wether your are crashing while using OpenCL.
In case you want to simply access GPU computing try “System Preferences > System > Activate Open CL” and you should be able to use your GPU… but be aware of SSS and HDR being not supported unless you use Blender 2.79 (current BETA?)