I am considering replacing an AMD Athlon 64 3500+ CPU with an AMD Athlon 64x2 4200+ CPU. It is in a Dell Optipex 740 desk top with standard heat sink and no CPU fan. I have three concerns. CPU power consumption and cooling and will I have to reinstall the operating system? I would like to do this without having to install a CPU fan. The computer will be used for mostly web browsing and playing facebook games. It is for my mothers computer and we would like to do it in the most cost effective way. Any help in this matter would be appreciated.