Have you booted from USB key?? If yes, please check the USB key connectivity.
ESXi once boots up, its in RAM of the server, which is non-persistent. It uses cron job to make the persistent changes in hard disk or USB key. EX# If you change ip address of the server, it will change, but for persistent change it has to go in boot media (hard disk or USB key).
Please check the device status.
-A