Need help with workstation pc difficult issues.

I’m using dell T3500, My workstation pc problem giving me white,black,orange screen and turn to sleep mode also automatically restarting while the power on and using the pc I tried too many troubleshooting and cleaning the pc and ram but still getting these issues specially the screen colors such us sometimes I find my screen turn to white screen while power on and everything is fine which gives me no choice except restarting the pc and that happens too many times per day or can be per hour.