Searchknow is a rather complex system and browser infector that typically requires multiple sequential steps to remove successfully. Because Searchknow arrives by bundling with another user-downloaded installation-based program, it is actually installed into the victim system using typical full-system privileges. This makes it harder to remove than some typical drive-by infection vacuumed up by a browser. One of Searchknow's system infection elements automatically acts to interfere with various 'normal' attempts at removing Searchknow, so you're probably going to have to kill that off using a special program (eg: Rkill) before you can get anything else permanently accomplished.
There's an excellent write-up at http://www.bleepingcomputer.com/virus-removal/search-know-ads-removal-guide which explains how the infection occurs and all the 25 or so steps that need to be done to be certain to totally remove the infection. It will involve you using a variety of free download tools, all of which are known to be reputable (as is the Bleeping Computer site itself).