Iphone troubleshooting

My iphone 3gs is turned on but the screen is black apart from my onscreen home button. (my home button dosent work but now the lock button isn't responding either, i can't do anything but the slider to turn my phone off keeps randomly appearing; so i slide it but it stays turned on just black. So i can't turn it off either or reset without neither buttons. It can't be to do with the screen because, when voice control comes on randomly, i can see the top strip with the time, battery life, signal etc.won't turn off, basically not really turned on since i can't use it.what's up with it? And does anyone know how to fix it? BTW this happened in class today, when someone rung me, so i quickly held in the lock button to turn off and when i got out of class i noticed the screen was black but urgh. I know the phones old and everything. Also its jailbroken but i'm sure thats nothing because it has been since the day i got it. Sorry its long please help.

It's the jailbreak that caused it. Same thing happened to my iPhone 4. The way I fixed it was to hold down the power and home button which forces the phone to reset. If your home button doesn't work, well you're a little bit screwed. You might have to restore with a backup, or reinstall iOS completely. Which gives a whole host of new problems (iOS 6.1.3 is more difficult to jailbreak).