I have had this problem happen twice now. I have a normally functioning server that has rebooted many times, and then I reboot it, and it never comes back. Instead of completely booting back up, it stops at a blinking cursor before it even loads GRUB or anything. It goes on indefinitely. In the BIOS, it appears that the UEFI boot device is not even there, even though the USB drive is visible. It's almost like its trying to boot in legacy mode off this UEFI drive. This is what happened a few days ago on the old and likely worn out stick drive, and ryecoaaron confirmed that the broken cpu temp plugin was not the problem. But now this is on a brand new stick drive, monitoring is not enabled, and the flashmemory plugin has been running the whole time.
I appreciate any guidance I am given, I'm at a loss here. Let me know if more information on what I have done to the server would be helpful.