It really depends on why it won't turn on, so we need more information.
For example, when you say "doesn't turn on", do you mean "doesn't respond at all" or "won't boot up"? Does the battery charge when you plug it in, or does the charging light come on? How old is the battery? What (if anything) happened before it stopped working: system update, phone dropped, attempted to root it,...? Has the phone ever got wet?
If it's completely unresponsive, won't turn on at all, and it isn't the battery, then there is nothing you can do except get it repaired or replaced. If it powers on but won't boot then there may be something, but we'll need to know exactly what it does do (and, as Tommy says, what type of phone it is) to have a chance of helping you.