How to put restricted areas or fields on same workbook until filing some fields first?

[dreammaker]

Dear Sirs,
I have Excel 2007 and I need a solution to put some restrictions for some fields until filling some another fields first,
ex.: I can't fill A2 before fill A1.

Thanks in advance for all helpers..

[Sindhus]

You can use data validation option. Select A2. Go to data validation --> Allow: Custom --> Formula: =A1<>0 .
Uncheck the "Ignore blank" checkbox.

[dreammaker]

DEEPLY THANKS Sindhus for your assist...