This happened randomly and out of nowhere? Not after installing any particular homebrew, themes, plugins, etc?
Assuming this is the case I would recommend formatting Flash1, which holds settings files for your PSP. I'm assuming whatever custom firmware you have installed has a recovery menu option? To access this you would normally turn your PSP completely off, then while holding R turn the PSP back on, and keep holding R until a menu comes up. On this menu, under Advanced I believe, there should be an option along the lines of "format flash1 & reset settings", choose this one. Then go back and hit Exit, which should reboot your PSP and hopefully fix the issue.
If this doesn't do it (or if the recovery menu isn't available on your particular custom firmware; I haven't used anything newer than 5.50 GEN myself), I would look into trying to reflash the custom firmware itself, most likely using the same installer you used to install it in the first place.
"I think that the problem with this video is it is highly derivative of many popular bands within the genre. Although when viewed on its own merits, it does have a deeper groove. However what it has in groove, it lacks in originality. One can't help but be reminded of such bands as Pearl Jam, White Zombie, Suicidal Tendencies and other bands that bear the mantle of so called "Alternative Rock". One is even reminded of Lorie Anderson when she wore curlers. Hehehmhm! This video speaks less to the heart and more to the sphincter. In closing, I think Korn would do well to learn more from -"