O man were do i start... Im trying to be as nice as possible but if i seem mean im not trying to be.

First off you need to correct the deposit and withdraw because i can deposit and withdraw using more than 2 digits after the decimal. I dont know about the uk but in us dollars money value cant go beyond the second digit after the decimal. I would use the DecimalFormat class(duh!!)<-Not making fun of you just the name says it all.

You need to set up a couple of try-catch blocks.
1.NumberFormatException: When i enter a string into the account details-deposit/withdraw text box i get a NumberFormatException.
I can enter a string into the account number box and get a NumberFormatException too.

2.StringIndexOutOfBoundsException: In the account details when i select No Account Selected and deposit and withdraw a value i get a StringIndexOutOfBounds exception.

Thats all the errors i have found up to now.
I will help you tomorrow with your code, but right now i have to get some shut-eye.