Why my engene light never came on? I heard a.

Why my engene light never came on? I heard a squiking noise coming from engine and so I replace the tension pully with new belt, but the noise was still there, so kept driving it had no problems untill about a month later it would not start, put a new batery and cables on it, turns over but still would not start. Put new timing chain and gears on it, now it starts but still making that alful wineing noise sounds like coming from lower part of engene, but what I dont understand is why the engene light never came on and the computer has always worked in telling me of any alerts?