If your Rok Box is prompting you to select a boot device when booting, the first thing to do is to remove any and all USB devices from the PC that might be affecting the boot process.
This is especially true of removing USB thumb drives and storage drives, as well as dongles such as iloks.
Remove them, power the system off, boot again.
If you continue to get the error about selecting a boot device, and if you do not see "Windows boot manager" as the first boot device in the boot menu, you should check your BIOS settings.
Reboot the PC, press DEL repeatedly as it boots to enter the BIOS/CMOS setup.
Once there, locate the "save and exit" tab -- if you do not see this, your BIOS may be in "easy mode". Enter advanced mode by hitting either F7 or F2 -- you'll see a note at the bottom of your screen that indicates how to enter advanced mode.
Once there, navigate to the save and exit tab, and select the option, "Load optimized defaults", then hit Enter to confirm.
Hit enter on "Exit saving changes", let the system reboot, and see if it boots normally.
If not, you may have an issue with your Windows installation, which would mean needing to troubleshoot the startup settings.
To do this, see this article:
Windows Boots to "Preparing Automatic Repair", but issues are not resolved
If none of these solutions work, please contact support.