How to keep track of transaction and calculation?

[Jon]

Greeting,
I have the following datasheet that I use to keep track of transaction for a
balance
SQ Incoming withdraw balance
1
800
2 ------ 300 500
3 200 ----- 700
4 400 ----- 1100
….

What I want to do is calculating the balance after each transaction and if
incoming transaction done the transaction withdraw is disable and if
transaction withdraw is done the incoming transaction is disable and message
box appears and inform that you can do both of transaction at the same time.
How to do that please??