Although rare, there are computers such as Acer which are not compatible with graphical PXE boot menus.
In “K2000 Settings and Maintenance” under “General Settings” there are three options for “Boot Manager Style:” Selecting the “Basic” option should repair this issue. This menu does not support using arrow keys to select menu options. You will need to type the letter combination corresponding to boot environment you need.
All other options such as using boot actions will not be affected but you can not lock down the menu with a password as you can with the other two selection.