What could be worng with Samsung Fridge Freezer SRS208?

Its a Samsung FF SR S208 CVW. Worked fine for 4 years and suddenly deforsted on us losing all food. Turned power on and off and it came back to life, gets down to set temperatures fine and stays there until (presumably) stat says "getting warm chill me down again" then it goes wobbly loights flash and warms up Every time I kill power it resets fine . Have it rigged on a socket timer so it resets every 3 hours or so it kind of works ok but there must be a fix for it. Is it a stat reset issue? will it be expensive? Any help please please please...its driving me nuts!