rpfaff, Error 5 means flash error.
Place thumb on rear left hand side of popup flash and apply light pressure to manual assist in it to open.
Now press the manual flash popup button and providing you still have pressure on the rear left hand side of the popup, it should lift, if not try wiggling flash gently while assisting it to open with thumb and index finger, while depressing popup button. When open you can give it a thorough cleaning around the flash body and the cavity it rest in with isopropyl alcohol dampened Q tip/cloth and blow out dust in the tiny release lever holes with canned dry air. Try flash, if still not operating check links below to see flash hinge screw removal, clean and lubricate,(lubricate very lightly).
https://www.youtube.com/watch?v=av3t5RNY5PY