if i remember correctly, if there are no paks, it may exit (not sure of this, though)
if there is only one pak, it automatically runs it (if the pak has errors, it may crash)
if there are 2 or more paks, it will show you a list, for you to choose.
As ruffnutts said (and me a few posts earlier) the paks must be in /data/local/share/openbor/Paks/