New system keeps rebooting

I am having a problem with my system rebooting all the time,I can’t even get the new drivers installed. I have a Gigabyte GA-7IXE M/B,AMD Thunderbird Slot A 850cpu,128mb pc133 and a aluminum case by Skyhawk. The first time I can usually boot to windows and start detecting new hardware then it start rebooting. Each time it reboots quicker and quicker to the point it reboots before it has finished post. Any help would be appreciated.