Office Desktop Applications, in particular, Begin to Run Slowly in Windows 10

It Was Most Obvious in Outlook Emails

Probably because that was my most frequent activity.  The slowdowns started happening a few hours after I did a reboot, and another reboot seemed like the only solution.

The symptoms were particularly noticeable when I had misspelled a word in an email and tried to right-click to correct it.   That right-click would take 2-3 or up to 6-7 seconds to have a pop-up menu appear, and maybe as long again for a suggested spelling to appear.  It wasn’t just for spell checking, though.  A right-click to select options of any sort behaved the same way.

Then I noticed the same thing was happening in Word, Excel and PowerPoint.

Trying to Find the Problem

I noticed that when this was happening and I launched Task Manager, by CPU usage was approaching if not hitting 100%.  I tried to find a service or program that was causing this, but what I saw instead were a handful of tasks hitting 30%-40% but were all “normal” things – Edge, Windows Explorer, etc.  This went on for days and I couldn’t figure it out at all.

Then I Noticed Something

When I had Task Manager running and had clicked on CPU to show most active tasks, one that I hadn’t noticed before would just appear for a few seconds with high CPU utilization and then fade into lower utilization, again and again.  It was Windows Shell Experience Host.  I finally figured out that this high CPU usage had a most unusual cause….

What Caused It and the Fix

The surprise was the cause.  I had found a great Windows background slide show of astronomy photographs.  Not that Windows was start struck but rather that it was a slide show as background.  I changed it to a static picture (I also tried a solid color) and poof! The problem disappeared.

Why? I can’t speak to that.

You are welcome!