Quite possibly you have experienced a browser hijacking.
Do a search for a file called HOSTS (no file extension)
Usually in C:\Windows\System32\drivers\etc\
You can open it in wordpad by right clicking it and using "open with"
Don't use notepad as it won't let you save again without adding a txt extension
If you see a whole bunch of entries then chances are you have been hijacked.
they'll look like this
192.168.0.10 www.someplace.com
You can safely delete these.
They tell your browser to redirect any attempt to go to www.someplace.com to the IP address listed.
Anything with a hash # in front is fine as it's just a comment.
If you DO find such entries, then there is probably a running process that will put them back as soon as you restart, so you need to run some anti-malware anti-trojan software to find the culprit.
Usually the redirect your startpage and any search engines like google, but it IS possible the get web addresses from your favourites as well.