First make a copy of the current file.
On the current file you only have to comment the line where the error is highlighted by placing a quote (apostrophe) at the beginning of it.
In the case of errors in an If loop you have to comment all the lines of the same from If to End If.
You need to change the line
Price = Nz(DLookup([Price], [OrderDetailsQ], "ProductDetailsID=" & Me.ProductCmb), 0)
in the following
Price = Nz(DLookup("[Price]", "[OrderDetailsQ]", "ProductDetailsID=" & Me.ProductCmb), 0)
Without a file it is difficult to verify where the problem originates from, if you can post it you must also indicate the form, query and report involved.
To edit a form you must use Structure mode. It seems a little difficult to help you with concrete advice without having the database available to test it.
To give a precise answer you would need to see the structure of the database. However, generally all you need to do is insert a button and use its click event to write the following code:
Private sub cmdOpenFile_Click()
On Error GoTo Error_cmdOpenFile
Application.FollowHyperlink "full...