One of the most common issues is related to the Razer Chroma software.
Do you use any items that might use that software?
If so you can first try just disabling the effects inD3.
|a.|Navigate to My Documents>Diablo III > D3Prefs.txt|
|b.|Edit DisableChromaEffects “0” to say DisableChromaEffects “1”|
|c.|SAVE|
|d.|Restart Game|
If that does not work, the known issues thread here has more info on the Razer software. Known Technical Support Issues - [Updated June 21, 2020!]