i've had many problems like this with Q3A. what i've found out is that it may be a conflict with mods you have loaded. if you don't have any mods loaded then it may be that your baseq3 folder has too many maps in it.
sounds crazy i know but when i encountered this problem, CPMA and OSP couldn't be in the main directory together. also, i've had the game quit on me when connecting to servers because i had too many maps in the baseq3 folder. wtf? so i would pull some maps out and it would work.
or you may have a bad 3rd party .pk3 file. the only way to find it is to take all the 3rd party .pk3s out and add, say, 10 back in at a time and see if the game fires up.
hope this helps. i'll check back...