If you changed security settings with resource groups and user groups, Frogabog is probably correct. One solution is to just add yourself to all user groups with a role of Super User.
If you haven't changed any security stuff, the most likely thing is that the Google extra changed a MODX System Setting and didn't change it back when uninstalled.
Check the "manager_theme" setting in System -> System Settings. The value should be set to: default.
If that doesn't do it, try reinstalling the extra. If that solves things, look at the modification dates in the System Settings table and see which settings it modified. You can ask here or look at a clean install of MODX to see what they should be set to after it's uninstalled.
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PLEASE, PLEASE specify the version of MODX you are using . . . PLEASE!
MODx info for everyone:
http://bobsguides.com/modx.html