Rice does absolutely nothing so don't waste your time wth rice!
Also, you've used up both of your claims extremely quickly? Maybe you should get one of those old nokias? Ha jokes aside, your best bet is to take it to a shop that does professional logic board cleaning, if they use a decent ultrasonic cleaner, it should be good, as long as they know what they are doing of course.
You could also go the DIY routine, but this isn't always successful and it's only a basic DIY fix, you should take apart the phone, and clean the logic board and all the cable connectors etc. with 99.9% isopropyl alcohol and a toothbrush, you could also put the logic board in a tub of isypropyl alcohol to displace any water etc.
I would highly recommend taking it to a shop though, as you may damage it taking it apart. :-)