How can I get a picture back on a 27"Sylvania TV Model # RLF351 AKO1?

I have a Sylvania televison, floor model. I had cable on the television for 2 yrs. After I discontinued the cable the television would not show a picture good enough to watch. It still has good sound. I was told it might be because of the cable being disconnected. I aslo bought an atenna and the picture still won't should right. There are no nobs on the back of this television to turn and i can't find the book that came with the tv. Can someone help me. Serial # 51327165 The manufacture was located in Greenville, TN Made in 1986