I have the following problem. My HDD started to die, so I decided to make a clean OS install on a new HDD. I already have Windows 10 installed on the PC, so I've created an installation USB stick as recommended by Windows and installed the OS on a new HDD. The Windows installer made a GPT disk and created a couple of partitions. Then the installation went fine and I get the new OS up and running and then I've found that it can't start without the USB stick in.
The PC can restart without the USB, but if you shut it down, it doesn't boot. BIOS system diagnostics shows that there is no active partition, which is (as far as I understand) a nonsence, because active partitions are relevant for MBR disks, but not for GPT ones. The old disk is formatted as MBR, so I've tried to format the new one as MBR as well, but the Windows Installer changes that to GPT anyway when creating partitions.
When the USB stick is in, it seem to boot from the HDD, because if I force BIOS to load from the stick, the windows install starts instead of normal Windows.
It also boots with the old HDD plugged in, but in this situation it can boot either from the old or from the new one. I don't see any consistent pattern here.
The BIOS is updated to the latest version available on the HP site for my PC (7.15 rev. A).
I understand that your PC will not boot after windows 10 clean installation.
Please try performing a BIOS defaults on your PC and check if it helps.
Turn off the computer and wait five seconds.
Press the Power button to start the computer and repeatedly press the F10 key to enter the BIOS setup menu.
On the BIOS Setup screen, press F9 to select and load the BIOS Setup Default settings.
Press F10 to Save and Exit.
Use the arrow keys to select Yes, then press Enter when asked Exit Saving Changes?
Follow the prompts to restart your computer.
If the issue still persists, Change the boot options to UEFI instead of legacy in BIOS.
Unfortunately, BIOS reset didn't work. As for making UEFI the default boot option, it's already set. However, I've noticed something strange related to resetting BIOS. When you turn on the PC, go to BIOS and then save and exit (or cancel changes and exit), the PC restarts. And then it starts without any problem. However, on the next power off/on we have the same situation with the PC not booting. So, it fails to boot only after a cold start. The BIOS diagnostics utility shows the boot failure all the time (after either cold or hot start).