Why won't my iphone turn on? How do i fix it?

My iphone is jailbroken. I was on the phone for about 15 minutes before this happened, I hung up and locked my phone. Its charged but it won't turn on… I tried holding down the power button for 30 seconds to reboot it, but nothing g happened, I plugged it in just in case the battery HAD died. Still nothing, any suggestions?

Yes, try entering then exiting DFU mode. If you don't already know what that is, it is a series of holding and releasing the home and lock buttons: that is a tutorial on youtube that will show you how.

Also, depending on the jailbreak software you used (i used redsn0w) there may or may not be a "just boot" button somewhere in the menu on your computer. This is mainly for a tethered jailbreak which you did not specify whether yours was tethered or not.

Try those out.