It could be because of how long it’s been dead, I would let it charge a few hours before coming back to it, and if that doesn’t work, then the battery may be dead and need replacing (psp are known for poor batteries). If it still doesn’t work, it may have an internal issue with the charging port or something like that. Hope this helps!

Sorry then, I don't know what happened to it... Someone else might, though.

It could have damaged something, but have you tried turning it on with no battery and just the charger plugged in?

Check to see if it has all 3 connectors for the battery to use on the back, and also is it an off brand battery?

Are they off brand batteries?

Not that I recommend doing it because you could corrupt or damage data and/or your system, but you could save and take out the battery while it's not charging to force it off...

I would suggest trying a different memory stick or if you're using a miscro SD memory stick, try a different adapter or/and SD card

If anyone wants to know how I fixed mine, I replaced my charger and battery (both off brand) which both went faulty in 3 weeks... Be careful when buying new batteries and chargers!

The yellow charger receptor where you plug it in could be broken too, if you can, you should compare the parts on your and your brothers PSP to see what the differences are, and let me know what you find.

Can you navigate the menu by moving the d-pad and hear the clicks it make as you move back and forth while the volume and the system are on?