official firmware 5.03 is required to load chickHEN correctly. just follow the instructions in the readme file. it is supposed to freeze as you described. thats just the way it works.
double check that you have the h.bin file in the root and the gifs and tiff in a folder inside the ms0:\PSP\PHOTO folder.
because of your original official firmware, your motherboard could either be completely or partially hackable, which means that you need to figure out exactly which one you have before attempting to install a custom firmware, or you may brick your psp.
once you get chickHEN loaded, download and run pspident. it will tell you exactly which mobo you have.
you can get it here:
PSPident 0.4 - Find out what PSP Motherboard you have., PSP Hacks - PSP Slim Hacks