Is there a problem or am I just a bad parent?

My three year old started school in August and every since then I've had nothing but complaints. He was and is the sweetest child at times.He has good days and bad days.On bad days he's violent,mouthy,bouncing off the walls, and very disobedient. At times he's downright scary. When he's out of control he hits, screams, and cries. I've tried all kinds of discipline from time out to taking away things he likes (tv,toys,games ect) I've even tried spanking but nothing works. He takes nothing serious. He smiles at me and at the same time his eyes look like he wants to run right through me. He hits me and runs into me when he cant get his way. He does the same things at school.He dosent get along with the other children and frankly most of them are afraid of him. He wants to be a good boy and cries when you tell him he's being bad. I try to be firm with him and don't let him get away with anything but at the same time let him know that he's loved butnothing works. It's embarassing to take him anywhere because of his behavior and everyone (including his teachers ) talk to me like I just let him do whatever he wants. Most of the time I'm frustrated to the point of tears. Am I a bad parent? HELP!