Levi, YouTube began moving away from needing Flash for videos last year. The new format uses the video streaming capabilities built in to HTML5 (the latest standard for displaying web pages).
I'm not sure what version of Internet Explorer you are running, but here is the instructions for resetting IE 11 from the Microsoft Web Site:
You can reset Internet Explorer settings to what they were when Internet Explorer was first installed on your PC
. This can be useful for troubleshooting problems that may be caused by settings changed after installation. Note that resetting Internet Explorer isn't reversible, and all previous settings are lost after reset.
Close all Internet Explorer windows. Select the Tools button, and then select Internet options.
Select the Advanced tab, and then select Reset.
In the Reset Internet Explorer Settings dialog box, select Reset.
When Internet Explorer finishes applying default settings, select Close, and then select OK. Restart your PC
to apply changes.