Good you have killed one XPE nuisance. If you did not see Windows boot manager in boot list, that means Windows 10 was not installed via uefi by previous user.  So now you should try switch bios to legacy mode, save the change, enter boot list again, there you will or should see hdd, dvd, usb listed in order.  Move hdd to the top of list, restart.  Hope this works out.  If still no, pls report back and we will problem shoot.
Earlier today i bought a optiplex 990 from a local reuse center (has windows 10 pro installed) but everytime i try and boot it up i get PXE-E61: Media test failure, check cable PXE-M0F: Exiting intel boot agent  No boot device found. Press any key to reboot the machine The cable is secured and in the right place . i switched from legacy to UEFI. I ran a system diagnostics and it said no problems found. What's wrong and what do i do ?
No boot device found optiplex 990