Roper refrigerator stopped working?

My Roper refrigerator stopped working today. I unplugged it, blew out the coils etc. plugged it back in and it went back to working. I checked on it throughout the day and it was cooling great. I just went back out to check it, and it had stopped. Unplugged it, plugged it back in and it went back to working. Weird thing, when I first went out and it was not working, it was making a hissing sound inside the lower unit. Any suggestions would be appreciated.