LCD failure -- that's what the flash pattern means. First thing to do is reseat and check the wiring harness that runs to the display panel. If it's damaged, replace it. If it appears OK, reseat (disconnect and reconnect both ends) and try again. If that doesn't solve the problem, try the display built in self test (hold D through powerup -- you should see a self-test displayed on screen. If you don't, replace the display panel.
Post the full system model (inspiron 7373, XPS 9330, etc) if you need further help.
Display panel is working and the self test result is ok. But still the same problem.
Dell - Inspiron 5559 - windows 10 - 64bit
Intel® Core™ i5-6200U Processor (3M Cache, up to 2.80 GHz)
Intel® HD Graphics 520