issues with updating from steam

having trouble installing patch/update via steam been aboutr 6 hours or so "updating steam" message box and "extracting package....." then I get, "update complete, launching steam" dialogue box then dissapears and quickly reappears again and repeats....got a good connection at about 45mbps internet.....please help

just close and relaunch steam

Yeah tried that and just repeats the cycle over again......sucks not being able to update