[gwynevans]

Check that you get the Red LED lighting to show it's charging.

One thing that's counter-intuitive is that it's tricky to work out if it's doing anything when booting, as the the screen doesn't clear when resetting/booting! Watch for the LED to flash yellow when starting up after a reset - if if doesn't, try using the power switch.

If you've got a PSP-compatible charger with barrel connector rather than a mini-USB connector, that should charge it too & faster than via USB. There's a good chance it's a combination of battery & it not booting because the power switch hasn't been slid - they're really hard to brick even when reflashing firmware, let alone just in normal use!