Hi Shifali,
The validation expression will allow only A to Z or a to z or 0 to 9 values, you just add the missing special characters in the expression which you feel that they can be added using keyboard, for time concend i haven't mentioned all....
and there is one more way to achive this
just remove the Not from the expression and instead of teh special characters type all teh numbers from A to Z & 0 to 9 integers to achive the result.
Thank you
Rahul