Are you creating a patch in manual mode? Can’t remember off the top of my head whether you need to press “preset” or not after entering “compare” mode, or whether it automatically switches to that mode.
Are you on the latest firmware (found in the pinned thread in the P5/10 section). Though the fact you say “banks” and “tens” sounds like you’re using a Prophet 6 not a Prophet 10 as the latter uses “groups”, “banks” and 8 “programs”.
Still, the procedure is the same:
Press and release “write”;
While “write” is flashing, press and release “global” to enter compare mode;
Press any of the numerical buttons (by itself) to audition that patch.
If you are on the P6, remember that the first 500 patches are factory ones and can’t be overwritten. Can’t recall if that means you can’t audition then in compare mode or not or whether it simply prohibits writing but still allows comparing.
If that doesn’t help, email sequential support as I’m out of ideas.