94 S10 Blazer heater problem

Well I am new to this forum and was hoping someone might be able to help me out.... A week ago my heater was working fine and I shut the vehicle off for a couple of hours and when we started it again no heater nothing it didn't even blow any air in any position. I even tried the AC and that didn't work either. Well the next day I went out and started it up again and it worked again like a dream then last night I was going to go out with some friends and when I started it again no heater at all. Hoping it would do the same thing again today I started it to drive it too work and no heat again nothing at all. Does anyone know what this might be??? I am hoping its not the heater itself but I would like to know what anyone else thinks this might be??? Much thanks.

just another post but I just checked and I have no coolant in my resivoir could that cause my heater not too work??? my vehicle isn't overheating at all and still running at normal temp but it is 25 degrees outside right now as well..... Also it never has a problem when its running and operating only when I shut the vehicle off and turn it back on and this is only the second time it has happened. Might there be a relay that turns it on thats bad??? I have general automotive knowledge but heaters are out of my range.....

hey i had the same problem in my 92 s10 it would kick on somtimes and quit others so i tested my blower motor and turned out it was bad replaced it for 20 bucks and i had heat once again so i would check the blower motor first then check your switch in your dash mabey the relay also but it sounds like the blower motor