My iPhone 4 won't turn on, What can i do?

So i'm having a bit of an odd problem with my iPhone. Yesterday it ran out of power and since then i haven't been able to turn it back on. When i plug it in to my computer or a wall charger it will flash to apple logo for about 15 seconds and then it just turns off again without reaching the home screen. However if i plug it into my docking station it powers on and goes to the reset screen where it tells me to plug it into iTunes but as soon as i disconnect it from the docking station it turns off again despite it saying it has 100% charge. I've tried doing the hold the sleep button for 2 seconds then hold the home button thing but that hasn't worked.getting it replaced will cost me £50 so i want to see if i can get it working any other way first so is there anything i should try first?

Try calling the apple store

It sounds like its gone back to factory mode as when the battery went it effected all the settings, maybe put it into your computer then go on iTunes and act as if its new and set it up again, good luck. X

Plug it into the docking station and when it powers up do a hard reset by holding down the lock and home button together for 10 seconds until you see the apple logo appear this may help as this sorts out loads of problems for ios devices.
If this does not work though you may have to plug it into the computer and do a full restore of the os.
And if this don't work then i would suggest taking the phone either to a repair shop or the apple store.

Step One
Open iTunes and connect the iPhone to your Mac or PC.

Step Two
Press and hold the Home button and the Sleep/Wake button at the same time.

Step Three
After exactly 10 seconds release the Sleep/Wake button. Continue holding the home button until you iTunes pops up a message telling you that it has detected an iPhone in recovery mode.