Hi Emma,
Ben and Ryan's advice are straight forward. I would disassemble the device completely, following the guide [guide|6610|here on ifixit.com]. It is not that difficult.
Put the logic board into a bath of isopropyl alcohol for 2 hours and then let it dry for one day, possibly on a heater (low temperature) or in any warm room.
Also, when cleaning the logic board and before drying it, look for any corrosion on the logic board or on/around the connectors (including the ribbon cable connectors, for example the short ribbon cable of the back camera). If you spot corrosion, clean these areas gently with a tooth brush together with isopropyl alcohol.
I would give it a shot. If it wouldn't work, you can still bring it to a repair shop.
Steffen