2001 Daewoo Nubira Heater Blower

My heater blower was working fine yesterday. This morn. is started car. no heater blower. I tried and tried to get it to come on. No luck. A little later my boyfriend went out to see what was wrong with it, it turned on fine and worked fine. Shut it off. Then waited for a while . Started car again. No heater blower. Do you know what the problem could be. It works only sporadically