My laptop (Dell Inspiron 15-3567) has a message where it states there is no bootable devices found. I have changed the boot sequence from UEFI to Legacy and back. I have disabled SATA operations (suggested by dell associate in another forum) and back to ACHI.
Product Name: iNSPIRON 15-3567
System BIOS: 01.06.00
sERVICE tAG: <Service tag removed>
Epsa: bUILD 4304.14 uefi rom
After pressing F12 it says: Operating System Loader has no signature. Incompatible with SecureBoot. All bootable devices failed Secure Boot verification.
My only available option is to Shutdown
There is another thread where someone where someone explains how to add a workaround boot option to use another Boot Manger to get your system running. If you can find it, try it out to see if it works since is has for some others.