Why does my PSP say to connect a usb cable, when there already is one connected?

ok im goin tell you something
they have not released a custom firmware for psp-3000
well they have the blue soft tool .. but it cost offer $20
if u want an emulater to play it for when u get it hacked and the games
http://kingisoz.forummotion.com/emulators-f2/psp-gameboy-gameboy-color-emulator-t12.htm
i own this website and this download is for custom firmware psp and i have almost every game ..
1. search for chick hen cfw enabler (an application that will let you run cfw in your psp 3000)
2. download gpSP gba emulator for psp http://pspaikousha.blogspot.com/2009/07/…
There is a reason as to why Pokemon Diamond is only avalable on DS and that is because Nintendo owns the rights to the game.
Sorry to tell you but you can not do anything on your PSP it can't already do cause you have a PSP 3000 on 5.51 firmware, only way a PSP 3000 can run any type of homebrew/emulators is it has to be on 5.03 firmware.
You can't play Pokemon Diamond on your PSP.
It's like how can you play Mario in a PlayStation?
The only way you can do this is installing a game boy emulator for you PSP.
But I hear the upcoming PSP Go is more lenient with future firmwares...
There might be a problem on your USB Cable.
I also experience that problem and at first I thought there was some problem on my PSP.
But it's the USB cable to blame. DVD Ripper can rip DVD to AVI MPEG WMV DivX H.264/MPEG-4 AVC MP4 MP3 WMA excellently.
Try to change your USB cable.
The problem may also be on the USB port of your computer.
Media Manager for PSP is what you need. It includes a 6 foot cable to connect the PSP and computer.
Depends on where you bring it, but you may be able to do it yourself. I would personally check with a Handheld tech support forum, like GamersThrone and get some help to possibly fix it yourself. Sometimes it can be really easy.