1. Blurry text...this sounds like some kind of browser hack...but that's just a guess. Do a complete virus/malware scan. 2. Having more than one image viewer at a time sounds to me like a recipe for trouble. Each one will try to have it's own way making changes to the registry...setting file associations...maybe one of them was installed from an unsafe source...there are probably other possibilities I haven't thought of yet. My choice would be to uninstall all of them...reboot...then choose one and see if the situation has improved. If you must try a different image viewer, uninstall what you have before installing another. Just my $.02.

I'm not much of a Windows user but after doing a brief search, I'd probably check display scaling in settings.

And try turning on "Let Windows try to fix apps so they’re not blurry.":

(Image from: https://support.microsoft.com/en-us/help/4091364/windows-10-fix-blurry-apps)

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As for image files not showing as icons you might see if anything in this thread helps:

https://www.gardenweb.com/discussions/5779219/how-do-i-fix-this-on-my-computer

Note there may be two places where you need to make changes.
(1) While browsing folders in File Explorer

(2) In the Upload Dialog

I don't think the image viewing programs are the problem, since I have them on my laptop without any problems. HP Cartogra I installed from a disc, and FastStone I've had for two years without a problem. I installed Double Commander after the problem started.

None of the solutions for the blurry text worked.

Try this for the blurry text. Enter cleartype (all one word) into search. Select Adjust ClearType. Make sure the box is checked, then follow the prompts.

For Windows Explorer display, go to the View tab and select small, medium, large, or extra large icons.

I had already turned on cleartext when I did the color calibration for my monitor.

For Windows Explorer display, when I select icons, I do not get pictures - I just get icons of the program that will open the pictures.

I changed the default photo viewer, and that did not affect the Explorer display.

If I use Edge, the text is NOT blurry, but I still cannot see photos when I try to post a photo, even when I select medium or large (or even extra large) icons.

I really do not want to use Edge as my primary browser, but I guess it does have some advantages, although I do not know why. I do not have IE on my computer, that I know of. Maybe I should install Opera.

IE should be in the start menu in the Windows Accessories folder, or type Internet Explorer in the search box. https://support.microsoft.com/en-us/help/17621/internet-explorer-downloads

For the blurry text, see if Step 2 in this Chrome help page fixes it. https://support.google.com/chrome/answer/95290?hl=en

The "smooth edge of screen fonts" in the "appearance" worked! Thanks so much for that - I don't think I would have found it on my own. Now I just have to get Windows Explorer fixed.

Click the icon where it says Options, and Folder Options will open. Go to the View tab, and make sure Always show icons, never thumbnails is unchecked.

Thanks again! That fixed it. I had no idea I needed to do that. Everything works correctly now.