What to do when I iPhone 4 won't turn on?

I was trying to put on a bumper case (the case that goes around) and when i took it off my iPhone won't turn on. And I was sure my iPhone was 70%

Holding down the home and power buttons simultaneously for 12 seconds or 20

Hold down the Home and Power Button for 12 Seconds

OR
1) Plug your phone into iTunes
2) It'll back up all of your information
3) Go to your iPhone in the Devices Tab
4) Click on the Summary Section
5) Click on Restore
6) This will wipe all of your data off of your phone
7) Click on the Restore button again and Select Restore from backup
8) You'll have all of your apps, Contacts, Calendar Information and everything you had on your iPhone prior to the restore