It all a bit extreme the so called expert answers given out, ripping phone apart, or replacing components linked to expensive parts.
It sounds to me like the phone has been put into DFU mode, either accidentally by pressing sleep and home in combination whilst trying to get it to work or whilst trying to jailbreak.
The simplest way to exit out of DFU mode is connect to iTunes via USB and let iTunes detect if phone is in recovery mode, and follow on screen instructions. Or if nothing is detected by iTunes hold down the Home and sleep/power buttons on the iPhone while connected to iTunes. Then just hit the power button and this should reboot the device as usual.
If the above doesn't work you can then explore further as outlined above,
It's a late reply but for clarity and for future reference try the simpler cheaper method above to recover your iphone