"Strike F1 to retry boot, F2 for setup utility"

It started when I was playing Overwatch then for some reason the screen completely froze. I wait for around a minute and then when I held down the power button to turn it off, a second before it turned off it showed blue screen saying error occured. Since that time my Pc have been running diagnostic, scanning,repairing but it always ended up in some extremely long black screen thats lasts hours so I turn it off. Then the next day when I turn on my pc it says "No bootable device" and under it "Strike F1 to retry boot, F2 for setup utility." I tried clicking F1 and it doesn't work, I get lead back to the same screen. I read somewhere to try doing ALT+TAB with E,F,B with Num Lock, Cap Lock, and Scroll Lock on but I just get a black screen.

My PC is Alienware x51 R2. I've had it for around 4 years now and all the specs of the PC is default. I am running Windows 10.