404-page not found

Hi i have been playing with wordpress for the past few months and slowly getting the hang of it.
Iv had a problem with my website every time i login in to my dashboard its coming up with a 404-page not found error then directing me to a yahoo search page below

https://au.search.yahoo.com/yhs/errorhandler?hspart=gt&hsimp=yhse-gt&q=sunshinecoastlawnmowing.com%2Fwp-content%2Fthemes%2Fevolve%2Flibrary%2Fmed&type=967150

Not sure what i can do, any advise would be greatly appreciated.
Cheers
Karl