You don't need to remove the power slider at all (in fact, you'll probably just end up breaking it).
What you should do to remove the board is:
* Remove the joystick cap
* Remove all screws
* Unseat the speakers, L and R buttons, and the haptic motor (very carefully)
* Disconnect the LCD ribbon cable
* Starting from the top and going counter-clockwize, lift the middle section of the plastic housing so that it separates from the front housing bit by bit. Continue until you are able to lift the PCB along with it. Once the top section as well as the USB connector on the bottom have been cleared, lift the PCB towards the right and it should slide right out. Be sure to free the ribbon cable.