HP Compaq 8200 Elite Intel i7 based PC suddenly stopped booting Ubuntu but can boot Windows

[Abygm1]

I have an Intel i7 based desktop (HP Compaq 8200 Elite) which I used to run on Ubuntu 14.04 for the past 4 years. Last week the Grub menu appeared but Ubuntu didn't boot. After couple of restarts the Grub menu also stopped appearing.   Just a blank screen with a blinking cursor. I connected a graphics card to eliminate the possibility of on-board graphics failure; but no good. 
I tried the following:

• Tried to boot the HP from an Ubuntu 18.04 pendrive - Didn't boot.
• Tried to boot the HP from another HDD with CentOS - Didn't boot.
• Connected an HDD with Win7 - System booted without any issue.
• Connected the Ubuntu HDD on my laptop - Ubuntu booted without any issue.

Assuming the issue is with by HP i7 desktop, I connected the Ubuntu hard disk drive on two other HP Compaq 8200 Elites, both running Windows. Both didn’t boot; similar behaviour; blank screen with blinking cursor. 

Then I connected Ubuntu hard disk drive to another Intel i7 based machine (not HP); which booted without any issue.

I am completely puzzled by this behavior. What could be wrong with the HP i7s desktops, which is stopping Linux from booting ?

[Lil_Boy_Blue]

Hi

Dunno.

https://support.hp.com/us-en/product/hp-compaq-8200-elite-small-form-factor-pc/5037931/bulletins-not...

Security Bulletin...    HPSBHF03595 rev. 6 - LoJax UE

Maybe an update ?

[Abygm1]

Thank you, Lil_Boy_Blue for the suggestion.

I tried various things including updating bios to v2.32. But no good.  Desktop is NOT able to boot ANY flavors of Linux; but able to boot Windows.

[JohnB577]

I have just done an install of Xubuntu 18.04.2 onto a HP Elite 8300 and to get to the login screen I have to press Ctrl Alt Delete *two* times to get it to progress on from seeing a black screen with a flashing cursor on the top left.   Once I do this it works perfectly.   This is with the EFI options enabled and legacy disabled.  

I installed from a dvd using the desktop's internal dvd drive.

This issue is not present when using Windows 10  1803.

So hope this helps someone.   I spent a lot of time trying different things in the BIOS to do with legacy and EFI boot options & then found all I had to do was Ctrl   Alt   Delete & repeat that once it had gone back to the flashing cursor.

[Abygm1]

Thank you JohnB577 for the response.  

It did't work for me; as ctrl+alt+del reboots the system and back to the blinking cursor..