Hi Awake,
I have a SonyEricsson W900 and had this problem once.
It appeared to be the software within the handset that has failed. You can try to remove your battery for about an hour then switch your phone back on.
You may also want to try and switch the phone on whilst the charger is in to give it a kick start.
Failing that, you may need to contact your service provider to see if any repair facilities are available through your manufacturers warranty.
I hope this helps.