First things first, hopefully it isn't too late. Get the phone dry. Not just the outside, but everything inside too. This means you'll need to open the phone, and dry it out some how. A good way is to leave it in a bag of uncooked rice for about 24 hours.
After you are completely sure the phone is as dry as the Sahara desert, try turning it on again. If it still doesn't turn on, You'll need to start replacing parts. Here are the first few I would suspect:
- Dock Connector
- Display Assembly
- Logic Board (bad news)
If it is the logic that went bad, then your best opportunity is to sell the working parts on eBay and using the money to buy a new phone.
EDIT: Don't use a hair dryer (or other heat source) to dry the phone, or you'll just ruin your phone.