I'm not a mechanic but I would remove the lamp and check the voltage at the connector. If you have 12v with the switch on then your lamp is blown.
Or you could just repalce the lamp because that is probably what it is. The lamp filament on the high beam side is probably burnt into, you have to replace the whole lamp.
You said your driving lights work off your high beam, do you mean like aux/fog lights spliced into the high beam switch? if that is the case then check/re check the swith and all conections... most likely a lose ground. I would recomend running a seperrate on'off switch for you aux lights.
I had this problem when I installed my apes, except in reverse only my high beam was working once I put everything back together. I replaced the bulb and checked voltage and all that jazz. Ended up being a pinched wire in the hand controls so I backed out the screws not enough to be loose but enough to relieve pressure and everything started working again I haven't had any problems since. Hopefully that helps.