input boxes

Hello, I'm an excel student that unfortunately hasn't quite grasped visual basic!

As part of my assignment I have the following code repeated throughout my work:

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Range("B8") = InputBox(prompt:="Please enter the Part No.")
empty_Check = IsEmpty(Range("B8"))
Do Until empty_Check = False
MsgBox ("You have not entered data"), 0
Range("B8") = InputBox(prompt:="Please enter the Part No.")
empty_Check = IsEmpty(Range("B8"))
Loop

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Unfortunately, no matter how I change my code I cannot get the "cancel" function to work on the input box. Whenever I try to change the code, my message boxes don't work correctly.

Please could someone help? Thankyou.