I believe that my problem was caused by faulty CMOS battery that I didn't change for 5 months.
Every time I booted my laptop I was ask to set time/date. After extensive reading (I'm not an expert, only end user) it seems like NVRAM has its "x-times" write cycle and every time new UEFI OS is installed it's written as well.
My default Boot entries were hdd, USB, floppy, other USB, CD.
One day my BIOS "count cycle" greyed out & zeroed to "0000 times". At first I thought that some virus might cause that but do viruses have access to BIOS, don't know.
No matter what I do, removing CMOS battery, pressing every keyboard combination possible found on internet at boot, resetting BIOS to defaults etc, it never restores to my previous boot options in BIOS.
When I power on laptop I set date/time in BIOS when exiting I get warning
"Bootable device was not found" [continue], after pressing it, I get 2 options
-boot menu (which is blank) & -application menu with 2 other options
-BIOS setup & -diagnostic screen.
Entering diagnostic screen it discovers my hdd and USBs when plugged. But when I go back to BIOS boot options there is nothing but floppy disk. No way to boot from hdd or usb even though it's discoverable in diagnostics.
In this case (don't know for sure), did my NVRAM after being fully overwritten turned BIOS into some safe mode and erased all my boot entries?
BIOS type Phoenix SecureCore Tiano.