OS Boot Manager is not found

[Oneoone]

I have HP Spectre x360 - 13-4005dx (ENERGY STAR) and I changed internal MSATA SSD. It returns "Boot device not found" and Hard disk error (3F0). I installed windows and again tried to change boot order but UEFI boot order can't be disabled to directly go onto Legacy Boot order, where notebook Hard Drive is on top. in UEFI Boot Order, when I enter on OS Boot Manager it returns " OS Boot Manager is not found", which is why I think, its not allowing to boot from HDD and returns the error 3FO. I updated the BIOS and installed windows 10, updated all drivers but yet no success.

However I got a temp way through by plugging in windows 10 bootable USB and it shows the boot option, which if no button pressed, picks the installed windows from HDD.

I think that OS Boot Manager needs to be installed and/or the UEFI boot to be completely disabled (although I disabled secure boot but didn't work) so that it boots from Legacy boot order.

I hope to find solution here as my last resort.

Regards and thanks in advance.

[WAWood]

@Oneoone 

In PCs with both an m.2 SSD and an HDD, the boot loader files, and generally the OS files as well, are installed to the m.2 SSD.  When you replaced that, of course your PC would not boot.

Then, you said you installed Win10 -- but if the PC could not find the m.2 SSD, did you install it to the HDD?

Then you said you disabled secure boot -- which you should have done in the first place -- and are now using legacy boot but from the SSD.

You need to disconnect the HDD and then see if you can reinstall Win10, this time, to the M.2 SSD.

IF that does not work, then you need to consider contacting HP Customer Support to order HP Recovery Media -- as that will reinstall the Win10 OS properly ...

If you live in the US or Canada, contact information is on this page: http://www8.hp.com/us/en/contact-hp/phone-assist.html#section1

If you live elsewhere, contact information is on this page: http://www8.hp.com/us/en/contact-hp/ww-contact-us.html

NOTE: After you get through, stay on the line until you are finally able to talk to some one -- it can take a while!

If you have trouble finding a phone number, then try: 1 (650) 857-1501.

You can also try contacting Tech Support directly using 1 (800) 474-6836.