In unRaid 4.6 after restarting the sever to add a drive by a Graceful Shutdown.  I now only get a blinking cursor on boot up.  It doesn't even get to the flash drive to start unRAID.  It goes through the controller check process and just just hangs with a blinking cursor.  Any Ideas.  Last party check was run last week with no reported errors.

I'm getting the same thing right now. I'm adding a new drive and unplugged the main power connector to the motherboard. When I rebooted I saw a screen saying it detected a new processor? Run setup or continue. Now I get a blinking cursor like it won't boot from the jump drive.

I got it now. I had to change bios settings for some reason. I just followed this below and it worked for me. Now to pre-clear the new drive and wait....

 

    On the Advanced tab

        Choose 'USB Configuration'

            Choose 'USB Mass Storage Device Configuration'

                Set the Emulation Type to Hard Disk

    On the Boot tab

        Choose 'Hard Disk Drives'

            Choose '1st Drive', select the USB Flash drive, and press enter

            Disable all other boot drives

        Choose 'Boot Device Priority'

            Set the 1st Boot Device as the USB Flash drive.

            Disable all other boot devices

 

Finally, press F10 to save your changes and reboot the server. The next time you turn on your server it should boot into unRAID automatically.

sounds like the USB drive got kicked from the "Default boot device."  Check the BIOS and see what it says.

Sorry to dig up an old thread, but I had nearly the same experience, and wanted to share my different solution.  My MB does not have the USB option the previous poster referenced.  The boot order settings were not sticking in the BIOS, and I was ending up at the blinking cursor screen as well.  I set up the configuration again, disabling all other boot devices except the USB drive, but this time also changed 'Boot Other Device' from Yes to No.  This booted straight off the unRAID USB key.  I will look into an MBR format as well on affected drives, but for now at least I can boot.