Phone needs to be repaired. Is it under warranty? If not you can pay to have it fixed out of warranty or attempt to fix by yourself. Replacing the speaker is fairly easy on the Desire if you are decent with that kind of thing and can find the part. Good luck.Nick
You will need to do a Factory Reset most likely. Can you access the OS at all? If not you will have to press a combo of buttons while powering the phone on.Most likely Vol Up + PowerHere is a video showing the process:
Sounds like the ear phone speaker is dead, you can pick up a new speaker on ebay. It may also be that the phone needs to factory reset...BUT.. back up all of your info, contacts, photos etc before doing as it will completely wipe the phone. I suggest using HTC sync to backup.
Switch your phone off and try again, other than that it may not be compatible with your phone!!I tried to download something once and google play told me my device wasn't suitable.