try pressing the HOME button at your xmb (your psp's main menu).
go to the umd driver option, and press left or right until you
reach the m33 or sony driver. either one should do. exit the
vshmenu.
if it does not have a vshmenu, completely shut of your psp (not
sleep). hold the R trigger, and turn on your psp. you should reach
a black and red recovery menu. go to configuration > umd driver
> press x until you reach the m33 or sony driver, either one
should do. exit the menu, exit the recovery menu