- Check the data source
First, make sure the data in the chart or graph is coming from the appropriate data source by checking the data source under the Chart Tools > Design tab > Data menu. - Refresh the data
If the data source appears correct, refresh the data by clicking the Refresh button with the blue circular arrow icon under the Chart Tools > Design tab > Data menu. - Reopen the file
If the data is still not visible, try re-opening the file. - Unlink the chart or graph
Lastly, if the data is still not showing, try un-linking the chart or graph from the original data source by clicking Chart Tools > Design tab > Data > Select Data > press the Delete key on the keyboard > click OK > Save.