Admin toolbar unstyled list
Have you tried turning off CSS aggregation and seeing what happens?

The fact that it's trying to load a stylesheet at "http://localhost/drupal/?og6o9k" makes me think it's an issue with how your public file system is setup. Like it tried to create a CSS file but failed. I would check which folder it's set to and make sure the permissions are correct.

It could also be an issue with the theme. Trying switching to another theme temporarily and see if that fixes things.

Lastly, you can try uninstalling and reinstalling a fresh version of Admin Menu.