boot - Stuck on POST screen while booting (power on/ restart)

Everything was working fine till yesterday, now it is stuck on the POST screen while I am powering on or, restart.

It is working only if I press ESC or Enter button, which takes me to diagnostics screen and the rest of the startup works as expected.
I am not getting any error or, any beep sound.

Model: Lenovo Thinkpad L460

OS: Ubuntu 16.04 LTS (Single boot only)

Thanks

Edit: Any multiple keypresses starting it normally.
Enter key taking me to bios options, f12 to the boot selection menu.