Hello You should be able to select a boot device manually. A USB device will typically show up as a hard drive when manually selecting a boot device. If it is not seeing it as available or able to boot from it then the media may not be properly formatted. You can try another USB port, media, or a different boot loader. You can find documentation about settings on the R310 support page. [URL] Thanks
I made a bootable usb i changed the BIOS to boot from a usb. It won't read it or save it as a bootable device. i have no idea what the next step is. I a new to this and trying to figure out what to do next. 
Dell R310 "no boot device avaiable"