I am searching for help from few days and couldnt get my answer to this.
I have installed Zorin OS 16 Lite on my Acer device over Windows 7. (Clean installed it)
I have been using it for more then 5 Months and everything was working perfectly.
But now when i start my device, the following screen shows up and doesnt let me boot the installed OS:
Were you always trying your Zorin or you installed it? Because reading No bootable device -- insert boot disk and press any key makes me think that you simply tried your Zorin while your boot disk was inserted. I don't remember my Zorin installation perfectly but when I plugged my USB stick with Zorin .iso I could start the installation normally from its installation interface, selecting Zorin on Boot section. Can't you retry installing Zorin as explained on Zorin official installation guide?