2003 Kia Sedona headlights blowing out

I have owned this van since Feb-08. I have not had any problems with the headlights until very recently. On my way home I turned on my headlights like usual after dark and I begin to notice people flickering their headlights at me. I discovered that my headlights were no longer on. I begin to mess with them and found my hi-beams to still be working. After I turned them off and them back on to see if I still had lights or not I discovered that now the hi-beams were also blowed-out. I took the van to a Kia dealership and (long story short) after they first told me my battery was no good, they then told me my alternator was no good, they finally replaced both the low and hi-beam bulbs. The lights worked fine on my way home. The next morning after I started the van and then turned them on to see if they were still working the lights came on for about a half second and then they both blowed out again. I'm very frustrated because the Kia mechanic can not figure out what caused this problem nor can he tell me how to fix it. If they cannot tell me how to fix my van who can? Any suggestions?? PS. The battery and the alternator both are okay; they tested out just fine.