If you have a dedicated GPU and using windows 10 the computer usually run em4 in intergrated gpu by default, causing the white screen. To change this press start and search for "Graphics Settings". Then press browse and search for em4.exe in Emergency 4's directory, then press Add.
After that choose Options as shown below and choose High Performance and hit Save.
This is the only solution I know, if it doesn't work then I have no idea how to fix it. Feel free to ask me if you don't understand my instructions