Ending Macro - Variable Range

The following macro pulls calculated data from another worksheet and then performs a calculation based on that copied over data, then moves down a row and repeats. It is currently set-up to go down 300 rows. I want it to stop after it hits an empty cell in column C, but have not been able to figure it out. Any help is appreciated.

Sub Backlog_Update()

'
' Backlog_Correction Macro
' Backlog Copy from International File.
'

'
Dim startRow As Integer
startRow = 2
endRow = 300

Do
    Windows("Daily_DSI_Report.xlsm").Activate
    Sheets("LCD").Select
    Range("A" & startRow).Select
    Selection.Copy
    Windows("DASHBOARDS-REPORT.XLS").Activate
    Range("T1").Select
    ActiveSheet.Paste
    Range("V2").Select
    Application.CutCopyMode = False
    Selection.Copy
    Windows("Daily_DSI_Report.xlsm").Activate
    Range("AG" & startRow).Select
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Range("B" & startRow).Select
    Application.CutCopyMode = False
    ActiveCell.FormulaR1C1 = "=IFERROR(IF(RC[1]-RC[31]<0,0,(RC[1]-RC[31])),0)"
    Range("A" & startRow).Select
    
    startRow = startRow + 1
    
Loop Until startRow > endRow
End Sub