i just got a 6003 professional and my guess would be to switch off the camera and remove the battery.
then try a different [charged] : - ) battery.
i am flying in the dark as i do not have an instruction manual - yet.
you might check to see that it is in the single exposure mode, not multi-exposure setting.
also maybe you inadvertantly switched camera to the locked position...
...i imagine you have already tried these and other steps...
the same thing happened to me last night trying to do a time exposure of a tree under parking lot lights...
...those are the steps i took (plus finally putting the lens cap on. i tried the shutter release and voilą the mirror came down and film advanced.
other than that experience with day time exposures and inside the house exposures the camera had worked flawlessly.
it is quite a step up from my 6002 in terms of versatility and features. shot hasselblad professionally for 30 years and would not go back...except for the SWC that shares the bag with it.
try those steps again...it may work. if not drop you might try a shop in New Jersey (973) 244-9662 - have not used them but was referred to by krimar rollei repair (have had excelent, reasonably pricd work done by mr. maralian in the past- he is now only doing later rollei model TLR work.
good luck, buena fortuna,
smiling gecko,aka kenneth
p.s been searching web and have not found source for a rolleiflex 6003 professional...any suggestions?