You forgot the code tags (</> button on the toolbar).
Typically this sort of problem can be solved by exiting the Arduino IDE and then deleting the C:\Users\Don\AppData\Local\Arduino15 folder (or just renaming it in case you want to revert the action). The next time you start the IDE it will create a new folder of that name. That is the location where hardware packages installed via Boards Manager are installed so you would need to reinstall any packages that you had previously installed via Boards Manager. It is also the location where your preferences settings are stored so you would need to reconfigure your preferences or just copy the original preferences.txt over the new one the IDE creates when the IDE is not running.
Please be very careful when deleting things on your computer. When in doubt back up!