My 3 year olds anger issues

Hi. I have a 3 year old daughter. She used to be the sweetest kid ever. I thought her behavior was the known terrible 2's until a few months ago. The main problem is her anger. When she gets into trouble or when I put her to bed at night or for a nap she hits things. When I say hits things I mean it. She will hit and kick her bedroom door for HOURS. I have tried everything from compassion, to talking, to time-outs, even an occasional spanking and nothing works and even grounding her and taking things away, rewards system for her being good.. She started punching the door and actually broke open the knuckles on her fingers (4 of them) and they were bleeding and she still kept hitting the door even though that had to have been painful. I have tried sitting down one on one with her and asking her why she is doing it. She replies she doesn't know.  The other night she kicked a hole in her door. What force she has for a 3 year old to kick a hole in a strong door. A big hole too. So we put a piece of sheet metal up so no more holes can be put into her door (For her safety of slicing herself up on broken sharp edges. She will last for hours.  She screams at the top of her lungs too the whole time. my neighbors can hear her at their house while inside. This is not healthy and not what a child is supposed to do around her age. I understand temper tantrums but I believe this is so much more. Does anyone know of any disorders that could affect her like that. She speaks very well. Always is talking, very smart. I am just tired and I feel bad because she is hurting herself. I am at a loss of what to do and what it might be. Anyone have any idea's?

[margypops]

I think that she needs some help she sounds distressed and a visit to the doctor would be good. When you say the trouble is her anger, could you give us a scenario of what happens ,like when she gets into trouble , what would it be about? This is extreme for a 3 year old and in my opinion she needs some help as something is upsetting her .Good Luck