sound like your not doing it right
did you place the 3.71 updater in the UPDATE folder with the Program and change the 3.71 update's name to 371.pbp
if you look at the Read me it should tell you this
here is the Files you need
http://www.psp-hacks.com/file/1277and heres what the readMe says
Installation instructions:
First method for both psp, the prefered when possible:
Requeriments: a fat psp slim with 3.52 M33-3 or 3.52 M33-4. Previous versions of M33 won't work,
due to a bug that affects them and OE; or a psp slim with 3.60 M33.
- Copy the UPDATE directory into /PSP/GAME/UPDATE and copy the EBOOT.PBP of the 3.71 Sony updater
there but with name "371.PBP". Note: the program will not even show if you copy it to a different folder than that.
- If you are in the fat psp, make sure you have configured the psp to run the game folder in the 3.XX kernel.
- Execute the program, it requires 78% of battery. If you have idstorage corrupted due to a downgrader, the program
will ask you to correct it automatically so the update can continue.
- Press X, and the Sony updater will begin. Sit and enjoy while Sony code installs 3.71 M33
- When finished, the updater will ask you to reboot (pressing X or O). DO IT. Do not skip this step
shutting down the psp by yourself, or you'll end with a brick.
- You should be now in 3.71 M33