My safari keeps opening by itself then every few seconds opens up another page with msn on it

1. Safari > Preferences > Extensions

Turn all extension off, relaunch Safari and test.

Turn those on one by one and test.

2. Safari > Preferences > Search > Search Engine :

Select your preferred search engine.

3. Use free AdwareMedic to remove adware

http://www.adwaremedic.com/index.php

Install , open, and run it by clicking “Scan for Adware” button to remove adware.

Once done, quit AdwareMedic.

or

Remove the adware manually by following the “HowTo” from Apple.

http://support.apple.com/en-us/HT203987