Chosen Solution
What can i do to repair it(Blue screen of Death)? Flash0 / font accidentally deleted :(
Make sure your charger is plugged in and press the O button to repair and restore default settings.
If you are actually running a CFW on the PSP, than you should be able to boot it into recovery mode holding the right bumper, while turning it on. If you were using a HEN, and don’t have a CFW installed, then you are kinda stuck with a brick, and might want to consider selling it for parts. EDIT If you are using Custom FirmWare (CFW) and can boot the PSP into recovery mode, using the method above, and you can scroll over to Advanced>Toggle USB (flash0), connect it to your computer via USB, and replace the font file you deleted.
I concur with ABCellars. To clear BSOD try pressing o The PSP will then attempt to repair itself by re–installing default settings to flash.