Why would you turn off the monitor during Memtest? The information shown is often critical for you to understand if you have errors. Try and press the reset button on your system and see if you can get back into BIOS. On another note, mind sharing your specs like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Was there any need for running memtest86? Did you encounter BSOD's when computing?