something tells me, if you own an HP, your trying to UNDERCLOCK, you dont know how to look in bios, and you ask for help w/out giving your computer specs, that you have no idea what you are doing. IE. You probably reinstalled thermal paste+heatsink wrong. IE you didnt take the old paste off (ill bet ya 100$ you didnt).
Anyway, i think your best bet is to check ur warranty, its a new chip so it should still be under warranty. If its not, go to a computer store, get a computer literate friend to apply new thermal paste IE artic silver to your CPU and apply the heatsink. Also make sure ur fan is running optimal. Also, ask the person at the computer store to check your temps w/ a meter. Your mothercard could be reading your temps wrong since a new heatsink w/ aftermarket thermal paste should run your cpu COOL.
Also never buy HP!