Locking cell when date is before 01.01.2011

Hello,
Any chance someone can help me with the formula. If for example in cell A1 is date that is equal or before 01.01.2011 i need to lock cell B1 so it would be impossible to input data in cell B1.
Thanks

Hello
Using data validation with this custom formula placed in B1.

=$A$1>DATE(2011,1,1)

Hope this helps.

Hello,
Thanks formquick reply but this onlt gives me True/False in b1

Hi
You need to select B1, go to Data Validation on the Ribbon. Settings tab, then in Allow drop down, select Custom and in Formula place the formula I described. You may add any messages you like here also. When you try to place a value in B1 and the date is less than or equal to 1/1/11 in A1, it should block any entry.

H-U-G-E Thanks for your help.

You're welcome , I should have made it clearer in my first reply.
Regards DBY