FRIG/FREEZER GETS COLD OFF/ON ... WHAT'S WRONG??? GE PROFILE S/S?

MY GE Profile side/side frig "works" but seems to get tired off and on. The lower part of the frig and freezer sections are cold, so I'm guessing it's the fan, but I really don't know. Sometimes the frig sounds right, so my guess is that something is working correctly at that time, but then it seems to not work. Sometimes the freezer does freeze things, and then a week later I'll notice the ice cream is soft. The frig is about 10 years old and if it's something that won't cost a fortune, I'll have it fixed, but if my frig is dying, I don't want to waste the money on a repair call. Help? (thanx :)