The HP t5135 has a standard Phoenix AwardBIOS - hit F10 on power-up to get into the BIOS setup screen.
The boot options are:
With the USB option set it booted Linux distributions from a Pen Drive.
The embedded operating system is HP's ThinConnect - a Linux variant based on kernel 2.6.24.
For BIOS version(s) see the BIOS versions page.