"No operating system found" Error! Help!

[OrangeBaller]

I tried to turn on my computer this morning and received the message "No operating system found in any of your devices. Press any key to retry."

I've seen many places online that give advice on how to fix this, but I'm technically challenged as to the different componenets of the PC. Can someone please let me know what the problem maybe, and give step-by-step instructions on how to proceed. Thanks!