well it doesnt sound like the playstation thing is new so if the behaviour is new it is something else....
playing playstation it self wont cause this behviour - it is the whole environment.
sounds like things are tense between you and the ex which understandable.
you can do some simple things with your child to see how he is thinking about things, have him draw a picture of his sfamily, of his home. see where /how he draws mum and dad.
have his teddies play school - or action men whatever characters - do role play a toy tkaing another toys things etc - how does the toy react? show him the appropriate reaction.
ask him why he hits/bites other kids.
the biting hitting being angry at you - prob he ahs picked up from ex something about blaming you why you are not together - something you can talk to him about, about having two homesetc how mum and dad dont get on but you both still love him etc.
all behaviour is communciaiton adn he is communicating he is a confused and angry little boy.
also, for small child associating one week long behviour with not getting playstation wont work - it needs ot be immediate, or use star charts during week. and it wont work with you asking the ex to deal out the pinishment -
you ahve to set rules in your hosue adn give immediate rewards for good behaviour - this is very important to reward every day soemthing he has done well or he has ate well or nicely etc...and have consequences for bad behaviour "today you hit johnny so we take away one star" -think super nanny type stuff, get some star charts going.
what he does with his dad is his dad's repsonsibility. but he needs ot know that mum's rules and teacher's rules appply.
ask health visitor about positive parenting /behaviour management for under fives courses in your area - they can be really helpful
you cant realy stop dad letting him play playstation - no point in seeing that as cause of everything. but he needs to elarn that you make certain rules and teachers do too - and you need to make a big thing of rewarding him every day for good behviour - rather than just focusing on the bad behaviour.
rewards and repurcussions for bad behviour need to be immediate ot have effect for a four year old. he isnt going to understand a punishment on sunday for something he did on wednesday before.
and you cannot ask dad to discipline him or withdraw treats on weekend for something that happened during his time with you.
if his behviour does not improve you can ask educaiotnal psychologist to visit him at nursery and suggest strategies of you can ask GP to refer for family therapy. you might need outside help to help him deal with waht is going on in his life.
above all -start praising and rewarding him (star chart - leading to eg a toy or treat) for all positive and good behaviour when he with you. every day think of something he has done nicely.