sign in to itunes store will not disappear and the whole IPad will not let me go into other screens till this pop up goes away. I have entered the password several times and still will not disappear. Turned the IPad on and off but the pop up remain

FIrst try a soft reset by holding down the home & sleep/wake buttons until the Apple logo appears then let go & let the iPad boot up normally.

If that doesn't help then to make sure you have a strong internet connection.

Try resetting Network Settings

Settings->General->Reset->Reset Network Settings,

You won't lose any data but will have to log back into your wifi networks.

Once logged back in and when the pop-up appears, try entering your password again.

Who told you to upgrade the storage account?