2001 Kia Spectra what could the problem be?

I have a 2001 kia spectra that I put alot of miles on for work. 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 schreeching sound when I accelerated til about 40 mph when it changed gears, also did this when I slowed down, plus when it did this the head lights would dim. So a couple months passed til finally 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 10 miles it went back to belts squelling 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?