Windows starts and opens but screen Flashes on and off

[mariah]

So here is my problem I have a toshiba laptop with windows 10 on it. It starts up I can log in however when the screen turns on you can see the background pic but no icons. Then the screen turns off and back on again showing some icons it does this a lot displaying and removing icons while the screen continuously flashes on and off. If I try to use cortana a box shows up saying it is not working and to close the program. I don't know what to do I tried safe mode, I tried to go back to a point where the computer was working fine but same problem and it says failure to complete I don't know what else I can think of. Any ideas???