Sounds like separation anxiety which most likely was a result from the person before you. A few things you can do is 1 put him in a pet carrier to relax small bits at a time while you are home, give him a blanket, 1 of his toys and a treat when he goes in, you will have to lead him in i am sure for a few times, sit close by at first keep him in there for about 5-10 mins tops don't give in to any cries. then start going out of sight when you have him go in for 10 mins , then after awhile should go in on his own, reward him when he goes in not when he comes out, needs to be done a few times a day. Don't kennel him for punishment this will defeat the task you want. After being left alone in the day spend first few mins with him and a treat is fine but make sure he is calm rub his belly and behind the ears to calm him then reward with a treat, don't spoil him you are the owner he is your pet not other way around.
Also do a control walk each day where he follows your comands not where he does what he wants, let him walk beside you not pulling you as he is out infront, don't be hitler with him on walk let him enjoy it at the pace you want not what he wants. When you want alone time like closed door like you talked about you can have him go in his kennel this will become his safe spt, over time with practice he will go there when you ask and lead him to his spot. Outside is the same he is away from you and has anxiety so he needs to be trained away from that type of action. He or she has gone through a major stress don't shock or you high pictched tools on them this makes things worse not a reward it is neg punishment i don't care on what anyone says about this. if he is real hyper talk to vet and explain his separation anxiety actions and ask about small doeses of ace to calm him for a shot time while he is being retraind. made for short term use.
Good luck many dogs have this and can be broke and will be of the actions just takes a little structured time.
Good Luck it will work just be consistant with reward system and make sure you are incharge not him.