To those of you that has got a 5.00 M33 CFW, DAX implemented a couple of new settings that allows to completely turn on/off plugins from the recovery menu. These settings are by default ON.
Try this:
Turn off your PSP completely (holding the power switch until it turns off), turn it back on and be quick to hold the R button to access the recovery menu. From here choose Advanced --> Advanced Configuration and try to disable the GAME plugins to see if it has any effect.