safari changes google to Yahoo?

You have adware/malware installed. Use  Malwarebytes Anti-Malware for Mac. It may be necessary to run more than one scan. After scanning a couple of times, restart the computer and test. If necessary, follow the manual instructions.  Do not download any other programs that are listed in the articles.  

See if the below helps. I would scroll down to the below or you might fall asleep.

Step 1. Eliminate Yahoo Redirect from Windows.    

Step 2. Delete Yahoo Redirect from Mac OS      

Step 3. Uninstall Yahoo Redirect from Internet Explorer      

Step 4. Remove Yahoo Redirect from Microsoft Edge.     

Step 5. Erase Yahoo Redirect from Mozilla Firefox.   

Step 6. Get rid of Yahoo Redirect from Google Chrome.    

Step 7. Eliminate Yahoo Redirect from Safari.   

https://www.2-spyware.com/remove-yahoo-redirect-virus.html.    

Go to Safari Preferences/Extensions, uninstall any you don't recognize, and then turn all extensions off. Test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.

 Safari/Preferences/General - see what the Home Page is set to. If something you don't recognize, see if you can replace it with something you want.

 Safari menu/Clear History.

 System Preferences and remove any Profiles you see.

Eric Root, I had yahoo redirect a few weeks ago, and I fixed the problem, but now safari isnt working all together, It says the application is open, but there are no windows, and it wont respond. Even after i tried option+command+escape and force quit it. I can't restart the laptop because of it, and not even the software updates can close it. Do you know what is wrong with my laptop? Is it virus releated?

You are welcome.