Windows Live Messenger now working! hellpp?

ok i use wlm everyday, and now i come on this morning and find its not there. i look through all programs and i go to the search yoru programs file and it shows nothing so them i try to redownload it and it says its still downloaded and so i turned of my computer to see if it didnt boot up correctly but it still doesnt show. you guys im so desprate plz help me