Okay so you have 2 scenerios here...One good, one bad...
Scenerio #1: You just need to charge your battery...Hook your PSP up to your A/C adapter, put in the battery and charge it...After about 1-2 hours...Give it a try by taking out A/C adapter and turning the PSP on using the batteries' power...
Scenerio #2: You somehow "killed" your battery...It no longer gives off a charge and therefore cannot make the connection with the PSP making it obsolete...You need a new battery to pandorize...
Here's hoping it's scenerio #1

...Hope everything goes well for you ..