Make Sure that All Minimum System Requirements are Installed
Disable Window Mode
Change Preferred & DNS Servers
Download-Install Driver Updates
Prevent Graphics Card from Overheating
Your graphics card may be overheating that's why Diablo 3 error 3003 problem persist. Take appropriate steps to prevent this situation and fix your problem completely.
Repair Game Settings
The recent changes made to the game settings may be the reason behind Diablo 3 error 3003. The settings are usually stored in the registry hives which needs to be repaired.
1. Download Diablo Registry Fix such as Reg in out.
2. Start a full scan.
3. Fix errors found in it.
The software Reginout is a great tool to optimize PC for gaming. It has an extreme gaming profile feature which lets your computer run fine by optimizing its services which helps to play game without any lagging or crashing.