Unlock a cell based on another cells value

[ryanusingexcel]

Hello
I have attached a sample of what I would like to create. I have colleagues who will populate the yellow shaded areas only if column 'A' has a loan number populated. All of the column 'A's will not always be completely full as in the example attached. So, I would like to only allow changes to the yellow shaded area assuming there is a loan number populated in column 'A'. Currently, I have the sheet protected so only the yellow areas can be changed, but I would like to see all of the yellow areas protected if there is nothing under column 'A'.

Anyone have any ideas?

There is no password to unprotect the sheet I have attached.

Thanks!