The issue might have been caused due to third party startup items or any other services. To troubleshoot the same, you would have to put your computer in clean boot state.
To help troubleshoot error messages and other issues, you can start Windows Vista or Windows 7 by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
Note: When you perform a clean boot, you may temporarily lose some functionality. When you start the computer as usual, the functionality returns. However, you may receive the original error message, or you may experience the original behavior.
Follow the below steps to put your computer in clean boot state:
Note If the computer is connected to a network, network policy settings may prevent you from following these steps. We strongly recommend that you do not use the System Configuration utility to modify the advanced boot options on the computer unless a Microsoft
support engineer directs you to do this. Doing this may make the computer unusable.
1. Log on to the computer by using an account that has administrator rights.
2. Click Start button, type msconfig.exe in the Start Search box, and then press ENTER to start the System Configuration Utility.
If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
3. On the General tab, click Selective Startup, and then click to clear the Load startup items check box. (The Use Original Boot.ini check box is unavailable.)
4. On the Services tab, click to select the Hide all Microsoft services check box, and then click Disable all.
Note Following this step lets Microsoft services continue to run. These services include Networking, Plug and Play, Event Logging, Error Reporting, and other services. If you disable these services, you may permanently delete all restore points. Do not do this
if you want to use the System Restore utility together with existing restore points.
5. Click OK, and then click Restart.
Now the system is in a clean boot state.
The above steps put your system in clean boot state. If you’re able to perform the backup operation in clean boot, it indicates that one of the services or startup items is corrupted and causing the issue.
Check the below link for more details on clean boot: