Removing it as the default search engine, and then deleting it as listed search engine, will only temporarily get rid of it. It will come back, as there is a virus running in your subsystem that is acting as a DNS redirector. Go into Firefox or Chrome, type some gibberish in your url bar, type enter, and boom, there is a Blekko generated search page all over again.
Type "google.com" into your url area, go directly to the google search page, then search for "Blekko redirect virus"
NOTE THAT MOST OF THE REMOVAL TOOLS YOU WILL FIND ON THE INTERNET ARE MORE THAN LIKELY VIRUS INSTALLERS THEMSELVES. I don't advise you use any of them.
Use something trusted, like Kapersky, or Vipre, or any other big gun, or best of all, remove all your personal data from the computer, and bite the bullet and do a complete reformat of your drive and reinstall Windows from scratch. I don't even use virus removal software myself any more, because none of it (even the best) can get rid of the more nasty psycho backdoor downloader viruses of today. You're only real option is to reformat and reinstall. It sucks hardcore but its the only sure way you know you got everything.