@ buffy_92,
If you are saying that everything is working fine now, great. If not, this sounds like an infection (malware), and I would follow the link given to you in post #17. Start with the Malwarebytes (MBAM) log and post it here...make sure you
UPDATE MBAM prior to scanning, then
quarantine any infection it finds. It actually can't hurt for you to do this now anyway because you mentioned something earlier about opening up FF and being redirected to Yahoo (if I understood correctly).
After posting your MBAM log, if there are problems, then I would proceed with the OTL log as directed on the link in post #17.
Make sure your Avast definitions and MS/Windows Updates are kept up to date.
You can also download something like CCleaner to remove unused files (cache, temporary Internet files, etc.) from your system, allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. There is a CCleaner
Slim Version http://www.piriform.com/ccleaner/builds - scroll down with no toolbars and requires less memory. Use this every time you are online and before you close your machine down to free up space as well.
Once you have everything working correctly, make a restore point in case you need to go back to a good configuration. You can set the restore point limit to a minimum amount if you like.