Cells lose formulas when data is deleted

Hi All and thanks in advance for your help.

I am creating a worksheet with (C1) quantity, (D1) item width,(E1) item length, (F1) which then calculates the square foot formula in the cell (WxH/144) or (D1*EC1/144), then we have G1, cost per square foot and finally, H1, unit total (C1*G1*F1). This goes all the way down the sheet with these formulas.

As we fill in the worksheet the calculations work fine but if you delete an entered value (number or cost) from a cell (say you entered the wrong price or width, it knocks the entire formula from the line, from both the cells that have been formatted to accept a formula.

I have protected the cells, worksheet and done everything that I can figure out but as soon as someone makes one deletion in a field, you cannot use that line's formulas any longer. When you zero the fields out, it sometimes happens and sometimes does not. This is a crapshoot and it is an important tool for us.

Please, can anyone help me???

Thanks,
Shawni

If we make a mistake entering data in the field and hit delete key or backspace say when entering the width or height item in that cell, the calculation in the next cell that figures the square footage based upon those entries disables and does not calculate the value from the formula tha that had been assigned.