HP Proliant Attempts Boot From Removable Drive
Some models of HP Proliant (such as the ML110 G5) will attempt to use a USB-attached removable drive as a boot device in preference to the internal hard disks. The issue appears to be that removable drive devices which are USB3-compatible are not detected properly for Proliant models which only support USB2. Instead of seeing them as removable drives in USB2 mode, they are detected as fixed drives.
To resolve, run the BIOS setup, and under Boot, lower the priority of the removable drive. If you have a number of removable drives, this may not need to be repeated for each drive if they are of the same model. The process may need to be repeated for removable drives of differing models.