Well, my friend drop her iphone into the toilet once. (yeah I know...(@o@ i) What she did to make it turn on again is this. After raise the phone, she put the phone into the rice container (Ewh...) Because rice can naturally abort water in the air. After a few day, her phone is back to normal. (Lucky... :) Good luck with yours!
I replace mine when I first got my MBP. In fact, the 500g drive fail to work. I can apple care and ask them why. They said that I have void the warranty at first. But I ask them, if by doing so void the warranty, why do they put the instruction in the manual? Anyhow, after a few chat, they agree that it does not void the warranty. They send me a replacement MBP because I told them it has problem with HD more than 250GB. The new replacement I got work perfectly. I don't know what happen to the first unit I got, but it only works with 250GB or below. it is very strange. So, I said check your manual for instruction and go for it. It doesn't has warranty seal for memory and hard drive. if this answer is helpful to you, I appreciate it if you can give me some score. thanks!
Perhaps you need to be more specific to your situation. Like Majesty said, the power button is on top right of the phone. However, if you still couldn't turn it on with that button. It means that your phone has very low battery. Try charging it for a few minute before you attempt to turn it on again. If after a while it still didn't turn on, then try hold the power button and the round button together for about 10 seconds. The apple logo should appear. if all else fail, try the genius bar at the apple store.