Three questions:
# Have you (re)flashed the BIOS with the latest version?
# Taken out and reseated RAM modules and swopped them around? Also run memory test, if possible? It may pin point the error.
# Connected the laptop to an external monitor or TV to see if the screen is defective?
Service Manual for your information:
https://dl.dell.com/topicspdf/alienware-17-r2_Service-Manual_en-us.pdf