Cannot boot after disk wipe

Help! I purchased a used Asus EP121 which the seller installed a non-activated version of Windows 10 on. After some research into drivers for 10, I decided to downgrade the tablet to Windows 8 and proceeded to wipe the disk, via an external optical drive using an old copy of Acronis True Image. All went smoothly, though I did foolishly allow the partitions to get wiped out along with the data, so not recovery partition anymore. When wipe was successful Acronis turned off the tablet. All normal. But when I hit the power button, the back-light flashes once then comes on, the optical drive (still holding the Acronis bootable dvd) spins up...but nothing else happens. Blank screen. So far I've tried restarting with and without power connected, with and without optical drive connected, with and without hitting ESC repeatedly, holding down Vol Down and power (this just caused the tablet to switch back off after a several seconds) and even tapping F9 (though without the recovery partition this is pointless), hit the tiny Reset switch between the USBs (which only works when running on battery only) and nothing seems to work. It won't boot from the optical drive and I can't get into Bios, or any other screens. Just back-lit blank black display. HELP! I just need this to boot from the external drive again so I can reload the operating system and make the tablet usable again. Can anyone help?