A few days ago when I started my PC I was greeted with this:

I didn't know what to do, so I hit CTRL ALT DELETE to just restart the PC, and it did.
From that time, and every time I start my PC now, it stops at the boot list until I select my SSD drive (windows).
After that, windows starts up just fine and I don't have any problems using my PC.

This is the boot list:
I consulted a friend about what EFI Shell is, and he told me that's what I saw in the first picture here.
We don't know why my PC tried booting like that, and now, even though I have completely disabled every possible boot option, EXCEPT my SSD drive, this is still happening.

Windows is starting up normally after I have selected my SSD drive in the list, but I am noticing performance issues, (games and applications that usually didn't impact my CPU too much, are now suddently eating up my CPU capacity completely).
But I have NO IDEA if that's in any way related to the boot issue.