Yesterday i dropped my Desire on the floor,it opened up and the battery got disconnected I tried rebooting the phone but nothing happens just getting the white HTC startup screen, tried wiping data and installing a new rom but nothing helps.
Anyone knows what happened and if I can fix it?

Try removing the sim and the sd card. Then , switch on the phone whilst holding the volume down button on the left of your desire.

Scroll to recovery and then select factory reset. You will lose all your apps but you should be able to reinstall the ones from the market

Hope this helps. Please post if it does.