hi. i saw a similar problem on a tp1500 comfort hmi, displaying no bootable device, please restart system. basically it is related to some hardware malfunction. if you see the mainboard, there present a NANDdrive BGA IC which look like a flash chip. that is the system drive(bootable media). it combines nand flash memories and its controller so acts like a normal SSD drive. the no bootable device problem  usually occurs when this chip is not correctly recognized or faulty device itself. the factory reset procedure can be done after these kinds of problems are solved. if you are familiar with circuit knowledge, see the circuit components around  the chip, check inductor beads, resistors and milo capacitors. also make sure the operation VCC to the chip is correctly present.

it's getting complicated but if all the matters above measure correctly you can doubt the faulty chip itself. to go further, you need a BGA rework station and gender socket for the chip, with which you can connect it to a PC like a normal IDE HDD drive. then you can confirm the chip is ok or not.

well, good luck

regard from Korea