|My guess is that you have the Transition option turned on.|
Depending on what version of Excel you are using, the Options dialog box is either under Tools...Options or under the Office button at the top left of the screen.
Turning off the Transition option should prevent the = sign from being automatically inserted into the formula bar.
The Transition Option is typically used so that Lotus 1-2-3 files can be opened in Excel. I can't say why you have it turned on (if that is indeed the problem) or how it will affect your spreadsheet if you turn it off, but I haven't seen it used in many, many, many years.
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