Use this file extract this from your computer and paste PSP-tools-v8 to your PSP-GAME and run it use this to format your magic memory stick but once you format your memory stick everything will be lost and make magic memory stick and to PANDORIZED your battery but you can convert the battery back to nomal again it's safe it woks with WINDOWS VISTA ...
http://dl.qj.net/PSP-Tool-v0.8-PSP-H...5555/catid/151


Now take all five official firmware from this site paste it to the ROOT of your memory stick where music,video,seplugins etc.....just paste it there from OFW 3.71, 3.80, 3.90, 4.01, and 5.00 all OFW then you can downgrade or uprade your PSP safe and try to use 1 gigabytes memory stick
http://www.psphero.com/download_official.html
good luck 100% safe LOL!!!!!