Changing the user name won’t matter, keep using the site as the admin user while debugging the issue. The best way to start investigating behavior like this is to check for conflicts with other stuff, specifically the plugins and themes. The way to do it is:
1. Deactivate (not delete) all your plugins and see if you still see the same behavior.
2. If the behavior is fixed with all plugins deactivated, then turn them on, one by one, checking each time you activate one if the behavior comes back. This is how you identify which plugin is causing the problem.
3. If deactivating all the plugins in step 1 didn’t fix the behavior, then keep all plugins deactivated and switch to the default TwentyEleven theme. Check to see if it fixes it. If it does, then it’s a problem with the theme.
If you still have the same problem even with all plugins deactivated and with TwentyEleven installed, then there’s something else going on. Come back here and let us know and please give a link to your site.
And yes, deactivating the plugins will change the behavior of your site while they are turned off. However it doesn’t delete any data; you will be able to restore the functionality when you activate them again.