first that could mean that you jail broke it wrong and you should hold the power button and the home button at the same time and you keep holding it untill the screen goes black and the apple pops up then just hold the home button.
Try to rejailbreak it. If that don't work try booting tethered. If all else fails, restore in iTunes and jailbreak again. Check apps from cydia before installing to be sure they are compatible with your device and iOS. I do a lot of JB and UL's. Biggest issue is people download older tweaks or apps in cydia that look cool without checking when the were developed or if they are compatible and then their phone don't reboot.