Do you've another antivirus, anti-malware, firewall or anything similar installed (or left-overs from uninstallations)?
The most common reason for problem of your type is that there is some kind of conflict between the two similar products.
If you aren't sure, I can check that in FRST logs.
Please, download Farbar Recovery Scan Tool (FRST) and save it on the desktop:
For 64 bits Windows: http://download.bleepingcomputer.com/farbar/FRST64.exe
For 32 bits Windows: http://download.bleepingcomputer.com/farbar/FRST.exe
Start the FRST program.
Read the disclaimer and click Yes to accept it.
Click Scan button.
When done, FRST will create two log files, called FRST.txt and Addition.txt, on the desktop.
Please, attach them to your reply (press More Reply Options button to see how to attach files).