My computer randomly freezes or restarts after i installed a new CPU,

[xxemann_101xx]

heat sink, and graphics card.? I recently installed a 3.0ghz AMD Phenom II Quad Core cpu, a zalman heatsink, and a Nvidia GTS 250 with Windows 7 Ultimate 64-bit operating system. Then my computer randomly started freezing, or restarting. So i took the lengths to re-install my operating system. Well, it randomly froze when trying to install. So after a painful 4 hours of getting halfway through install and have it freeze and then reboot and freeze and reboot, I got it to successfully install. Then with high hopes I started re-installing iTunes, steam, firefox, avast, all that good stuff, to have it freeze. So I rebooted, and tried re-installing everything one at a time, froze. Any ideas? I'm at wits end and about to lose sanity