White Screen of Death - LCD fine but still not working

Hi - been trying to fix an old 3GS for use at the gym etc. Its a strange one - I think it might have had water damage. When I got it, it wouldnt even recognise in Itunes or do anything apart from white screen. I have tkaen it apart - checked the screen works on a working 3GS so no issue there. I cleaned all the contacts and things like the vibration motor and sound are now working. I have done all the hard resets, volume/home/power, battery out, cleaned everything with alcohol. If I take pictures on the phone and import via usb they show the right screens etc. Any ideas?