iPhone touch screen not working after i launch an app

So this problem happened on my phone yesterday , right after i launch an app and quit it , the screen will go dim and touch screen not functioning at all but the assistive touch is still working pretty well and lockscreen is working pretty good too . I can only use the Sbsetting ( jailbreak app ) to respring my phone and the same thing happen all the time .


Phone: iPhone 3gs ( jailbroken )

anyone know what's going on ? Please help me :(