Excel or Outlook takes a long time opening file

1. Click Start then click Computer.

2. Click Organize.

3. Select Layout, and then click to clear Preview pane.

4. Open the Excel workbook and test.

If the error continues to occur, go to the next method.

Windows Explorer:

1. Right click on Start button

2. Click Open Windows Explorer

3. Click Organize | Layout

4. Uncheck Details Pane and Preview Pane

Excel:

1. Click File | Open

2. Click Organize | Layout

3. Uncheck Details Pane and Preview Pane

Outlook:

1. Open a new e-mail

2. In the "Include" group on the Ribbon, click Attach File

3. Click Organize | Layout

4. Uncheck Details Pane and Preview Pane

Source
https://support.microsoft.com/en-us/kb/2779852
http://geniustechbar.blogspot.com/2013/03/excel-cannot-complete-this-task-with.html