after replacing the serpentine belt I get loss of power with the presence of a squeeling. The car wont heat up if I use the heat before it is warm. squeeling goes away most of time when car is warm???

Most likely one of the pulleys is seizing up and causing the squeeling or your belt is not tight enough and is slipping. Chek the tension on the belt and if any of the pulleys are overheating.

Belt squealing - The belt tensioner is old and the spring is worn out. It is not holding the belt tight. When you start the engine, the alternator is sending extra power to recharge the battery. Add the blower motor and rear window defrost and the belt starts making noise. --- Since you are using the blower motor and rear defroster, I can assume that it is cold where you live. It's normal for a engine to warm up slower when it's cold out. It should be up to operating temperature after 15-20 minutes of driving. If it takes a lot longer than that, you may have a thermostat that is stuck open.

If you can locate belt tension pulley spring spray a little w-d 40 on it. And if you can exercise the spring by moving the pulley arm, if it is semi seized it may loosen it up. There might be a place on that with a half inch square hole where a tool will fit into to help do this. Or maybe a wooden pry, be carfull not to break any thing though. Hopefully your new belt is not one size too long..