My browser redirects me to spam pages often

My browser redirects me to spam pages often. I suspect its some sort of undetected virus.
I also remember I did that mistake downloading exe from unreliable source and running it and this issue started right away.
I tired to reinstall browser still same. What can I do?
Without reinstalling windows something simpler would be nice.

I use adaware antivirus free.

Removed adaware
Installed Eset interface was broken.
Removed Eset.
Installed Malwarebytes full scan got sth. in Firefox files, removed. Firefox was broken so that reinstall failed to fix. Whatever.
Now writing from IE Malwarebytes hit something inside it too upon open. Seems that problem is gone.