When your dimmer switch is in the neutral position that would be the low beam. When the switch is toggled up, it is your high beam. There is just a high and a neutral (low beam) position. Apparently your low beam is working correctly.
Try to do a quick test with your high beam flash switch (the button above your dimmer switch). If your high beam illuminates when you press your high beam flash, that indicates a problem with the actual dimmer switch. The reason why I say that is because your low beams are working, which indicates there is power to the dimmer switch.
If your high beams do not illuminate when you push the high beam flash I would suspect either the high beam bulb and/or indicator bulb is burned out or the wiring (blue/white wire) and connectors that leads from the dimmer switch to your headlight/indicator bulb is faulty. What the high beam flash switch does is bypass your dimmer switch so that the high beam should work regardless of the dimmer switch condition or the headlight switch position.
I hope this makes some sense.
Pete