Upgrading my Compaq 5BW120

Hello, I was in the process of upgrading my Compaq with a faster processor a 1.2ghz celeron using upgradeware adapter but after the install and I log on IE after about 5min the system freezes, I have done everything but reload the operating system which I dont think is the problem, maybe the processor itself since it only occurs when the processor is installed. So I am wondering would it be better for me to leave the system stock and sell or purchase a new motherboard and bigger processor. Your thoughts and opinions are appreciated. Do you have recommendations on a motherboard and processor that is not top of the line but something good for the basic email, IE, Office programs no major gaming.