My laptop- Dell XPS L502X -has started having screen issues. The screen flickers at first then goes blank for a random amount of time. It gets longer and longer as time progresses. I have run Dell diagnostics and updated the Intel graphics card drivers and the nvidia drivers. I have also run a long start up diagnostic. Everything has passed. I have had to hard boot it a couple of times because it never came back from blank. Each time it does go blank the sound still works perfectly. Any ideas?