Jailbroken iphone 3g frozen screen

try reset the os with dfu
https://icegolem.com/iphone-stuck-on-apple-logo/

Reset it with the home and power buttons until it shows the apple logo. If not, put it in DFU mode, but it will erase everything you have.

If your iPhone is jailbroken and you pressed reset all content, the phone will really not load and will be stuck on the apple logo. What you have to do now is to restore the phone using iTunes. To be able for iTunes to detect your iPhone in recovery mode and enable you to restore, you have to enter dfu mode. Just press the home button and sleep button simultaneously for 10 seconds then release the sleep button but still hold the home button until iTunes can detect the phone. Then press restore and let it do the rest of the process.

Could be charger, charging cord or the battery needs replacing

Try restoring the iPhone again.

http://jacko0.wordpress.com/2009/12/19/how-to-reset-an-unresponsive-iphone-and-get-it-working-again/

If your iPhone has firmware version 3.1.3 you can't unlock it yet. If it's lower version follow the iclarified website

Yup - your battery is fubar.

I'll recommend you re-break your phone and if you are willing to perform the task in a more simple yet time-saving manner, follow the step by step guide from this website: iphoneunlockeasily.com

Try to reinstall a jailbroken version of the iPhone OS.
Do not (ever) use reset to factory if you need the device to be jailbroken to function (e.g. in case you are using an officially unsupported operator/plan)

2g solution


3g solution

if it still gives you problems then you have a hardware issue, apple won't touch a jailbroken iphone so hopfully you have the apple care protection. Restore it to factory settings and try to take it in for service.