I lived in the us as an aupair and had a bank account with cheques and a card. There was no money or very little on the account when I left and I just forgot about it. I was wondering what happens to old accounts like this. Thanks

A checking account probably has monthly fees and would eventually be disabled after the balance is depleted, they should send some warnings before that takes place.

They make use of old unused accounts

But it happened to me once i didnt use bank acount for 5 years and went to check it they told me that i should deal with the main branch not the old branch i used to deal with and my momey increased

You abandoned the account. Eventually the bank closes inactive accounts and turns the money over to the state.

Eventually is turned over to the state as abandoned

If there is no amount for renewable fees then your account will be closed

escheat, assuming account maintenance fees haven't drained away all the money.

Depends upon in which country you live.