2001 Kia Spectra screeching sound and lights dimming

Recently I had both belts (power steering, which had broke the alternator) replaced. I thought that I had accomplished something. But soon as I drove it, I noticed a screaming screeching sound when I accelerated till about 40 mph when it changed gears and it did this when I slowed down, plus when it did this the head lights would dim. A couple of months passed and then my new alternator belt broke. I assumed it must need a new alternator, so I replaced the old with a new one thinking this should do the trick. Unfortunately it only seemed better at first but after driving it about ten miles it went back to belts squalling and head lights dimming again. I talked to some buddies and as far as anybody can tell they think maybe some electrical problem causing this. Any suggestions?