For some reason I can’t see the smoke simulation in my view port in the 3d view It renders but it won’t simulate when I play my timeline. It strange it was working before. I reinstalled Blender and it didn’t fix it.
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Moved to correct support forum
Can you maybe upload the blendfile, so others can try to reproduce the problem?
Otherwise, i think it will be just wild guessing 
Ohter informations would be helpful too. Like for example the blender version you are using.
I had the same problem, it was an graphic card’s driver issue.