If Outlook 2010 is automatically starting in safe mode, then it is likely caused by by a Windows Update (KB3114409). It can also be caused by a previous/new install that has over written existing Outlook files. This does not means, that you will lose your e-mails because they are either stored in the PST or OST files. If you are not using a POP account but an IMAP, then this is stored in your e-mail provider’s web server. There are two steps to fix this issue, the first one is to do a system restore to the point when it worked, and the second one is if there is no restore point, then copy/paste the files for the Outlook folder from the previous versions. Steps listed here are applicable to Windows Vista / 7 / 8 / 8.1 and 10.
Before proceeding with any of the steps, if you’ve got this update installed, then uninstalling it would be the first step. Hold the Windows Key and Press R. In the run dialog, type appwiz.cpl and click OK. Then from the left pane, choose view installed updates, in the search bar, type KB3114409. If this update is found, uninstall it and test. If it is not found, then proceed with the two methods listed below below.
Method 1: Restore Your Computer Using System Restore
Hold the Windows Key and Press R. Type rstrui.exe and Click OK.
In the System Restore window click OK. Click on Show More Restore Points, and locate a point when the Outlook was working, then choose that restore point, and proceed with instructions on screen to restore the computer to an earlier time. Once this is done, the system will begin restoring. After the restore has finished, check to see if Outlook works or not, if it doesn’t then proceed to Method 2.
Method 2: Restore A Previous Version
Click Start and type Outlook.exe in the search dialog. Right click on it and choose Properties.
Then go to the Previous Versions tab, and locate the Outlook.exe file that has date when it worked. Click Open to see if it works and opens without Safe Mode. Make sure the non-working Outlook that previously opened in Safe Mode is closed, because we are now running one of the copies saved in the previous versions. Do the same for all versions listed there, Open/Close until you see the one that opens without Safe Mode. If it does work, then keep the Window open.
Assuming that you now have the version of Outlook running, without Safe Mode from one of the previous versions. Hold the Windows Key and Press R. Type taskmgr and Click OK.
In the Task Manager Window, Go to the Process Tab, locate Outlook.exe, right click on it and choose Open File Location.
This will take you to the Windows Explorer, in \\restore point\…\\\Office(version). Copy all the files from here, click anywhere inside the window and press CTRL + A , then CTRL + C – Now this is from a restore directory, what we need to look for here is the path, and go to the current directory for Outlook to paste the files we copied. Make sure Outlook is closed, and go to C:\Program Files (x86)\Microsoft Office\Office 14 (look for the exact path from the restored version) and go into the directory. Once in the directory, paste all the files by doing CTRL + V. Now re-open Outlook and it should work.