1. Power on FREDL and press the "F2" key repeatedly to enter the BIOS setup. Use the arrow keys or mouse to select "Setup Utility".
2. This is the menu you'll see.
3. Use arrow keys or mouse to move selection down to "Boot" and select "EFI".
4. The EFI boot menu will likely show that a PXE device is the top boot option.
5. Press "F5" or "F6" to move "Windows Boot Manager" to the top position.
6. Press "F10" and then "Enter" to save and exit.
The system should now boot to the OS drive rather than attempting to boot to a PXE network.
Although your disk is recognized in the BIOS, it seems like it's not recognized as a boot device. Therefore the BIOS tries to boot from the network, which of course fails.
It seems like your disk has experienced a catastrophic error. In any case, there was no reason to change from EFI mode to Legacy, since your existing installation was probably installed in EFI.
If you have a Windows 10 boot media, use it to try and do Startup Repair.
If Startup Repair is impossible because it cannot detect a Windows installation on the disk, you should first try to save any data on the disk for which you have no backup. If you have a Linux Live boot media, this can be used for this.
The best next step in this worse case is to replace the hard disk. If you would rather try to salvage it, use the Windows boot media to reformat the disk. Use slow format, meaning not a fast format, which will take some time on a large disk, but may detect and mark the bad sectors. Install then Windows again, then check the disk health via its SMART data [one such utility is Speccy] to see if didn't have too many errors to use safely.