My GPU randomly shuts off then strats again.

I just want to say its radeon rx 570 sapphire nitro. So I'm actually struggling typing this question because it randomly shuts of. The screen goes black and then comes on again. the monitor does not turn of just becomes black. Sometimes the whole screen flickers with green and pink and sometimes while works it has white dots/pixels over the screen like 10-15 not many. Someone pls help me because I need to use my PC