How to Troubleshoot Excel's Autofill

1. Check your formulas for formatting errors. Ensure that all parentheses in your formula are part of a matching pair and enclose all nonalphabetic characters within single quotation marks. Always enter unformatted numbers in your formulas; for example, '$1,000' should be entered as '1000.' The numbers in cells can be formatted at a later time using the 'Format' menu.
2. Avoid losing data in cells when dragging the fill handle by changing your preferences. Under the 'File' tab, select 'Excel' then click 'Options.' Click 'Advanced' then click the checkbox labeled 'Alert before overwriting cells.'
3. Set calculations to 'Automatic' or formulas will not recalculate as you fill cells. To do this, click the 'File' tab, then select 'Excel' and click 'Options.' Select the 'Formulas' category, then under 'Calculation Options' choose the setting labeled 'Workbook Calculation.' Click 'Automatic' to have the formulas automatically recalculate.
4. Disable autofill by selecting 'Excel' under the 'File' tab and clicking 'Options.' Choose 'Advanced', then uncheck the box labeled 'Enable AutoComplete for cell values.'