My iPhone 3GS on jailbroken iOS 4.3.5 just "died" and showed a yellow screen when trying to charge it or turn it on. I found some solutions on the web, but none of them worked. Here is what worked for me:
1. Connect the iPhone to your computer
2. Open iTunes
3. Put the iPhone in DFU mode (if you don't how to that, google it)
4. Let it charge for about 15 minutes
5. Go to iTunes and restore the iPhone
Hope this will help someone...