loading the orig. gta umd on a PSP 1.5

hi,

i have searched so many forums, but i couldn't find help. my question is not iso-related (most threads deal about that).

i have the original GTA UMD and a PSP 1.5 and i want to load the game from the UMD, but i can't make it.
i have copied the mph 2.0 loader v1.1 on my stick and the firmware files (\mphgameloader\flash0 and flash1 [...]).
i even downloaded some of the "all you need to play gta on a 1.5" archives, which just contain a ready setup memstick with the loader + firmware files.

but the UMD won't start. i just turn on the PSp, then go to the MPHLoader, but the PSP freezes.

what am i doing wron?