Hello LocknLoad,
From what I gather, there’s an issue with your iMac sleeping when logged in to a specific user account. The article linked below provides user specific troubleshooting tips that can help you resolve the sleep issue with your iMac.
OS X: When your Mac doesn't sleep or wake - Apple Support
Try another user account
Try creating another user account, or log in as guest. See if your computer sleeps and wakes properly from the additional user account. If it does, your issue may be related to one of the following:
You can disable login items from the Accounts pane of System Preferences. Try opening only one app at a time in the original user account to determine which app is preventing sleep. If you isolate the issue to a particular app or login item, check its documentation, or contact the developer of that software for more information.
Ciao,
-Jason