If preceding cell in a column is blank, block input in current cell.

Hello,
I am trying to make a daily interest calculating loan sheet.
All the calculations(interest, payment and final balance) are triggered when the date is input in col. B
The IF function first checks for the date and then checks for any payment made. Only then it calculates the interest upto that day.
Problem:
If I miss a date in one row but continue to enter the date and payments in subsequent rows, the interest calculations are not resumed after "blank date cell"
What I want:
If a date cell is left blank then any data input in subsequent rows should be blocked.

I am not very good a VBA so any such solution will have to be explained thoroughly.
Thanks in advance.
I am attaching the excel sheet