ECS MB, CELRON 800, PC FREEZES AT BOOT

I am having a problem with my computer freezing up right when it first boots up… I can sometimes enter into the bios but after about 1 min it freezes. I have flashed the bios with the most current version. I have also unhooked everything to see ifit was memory or some other piece of hardware. I am thinking it might be the pwr supply. Any help is well appreciated. System is an ECS MB with Celeron 800. 512 MB PC133 RAM.