Aspire E14 - E5-473G-782R UEFI Boot Problem

So, suddenly I got this problem:

When I tried to turn on my laptop, I got an error "No Bootable Device".

I found out that changing my boot to Legacy seems to be doing the trick.

My last time turning my laptop on was a month ago. I bought my laptop 2 years ago.
I don't use my laptop often, because I have PC on my work place, but still I use it when I'm at home.

I've never change BIOS settings, and it's been working properly for these 2 years.

One of the solution I've think of is:
1. Backup all of my data
2. Re-install windows 10

What I want to ask is, how did this happen?
I don' know if I installed it on Legacy or UEFI, but the last time I use it, I don't change any od the BIOS settings and it is still working just fine.

Thank you