Hold the Sleep/Wake and Home buttons together until you see the Apple Logo. Let me know.
I was not sure from your question sorry. Where did you purchase the phone?
Ok you would have to ask them about any extended warranty you may have, but Apple's is only one year and it does not cover accidental damage or water unless you purchased AppleCare (then 3 years and some coverage)....you can check if you have your serial number: https://checkcoverage.apple.com