recently purchased a brand new amd athlon II X4 640 95w 3.0ghz processor for my m4a78lt-m le mobo. i previously had an amd athlon II X2 255 3.1ghz in it, but wanted a quad core. did my research, upgraded my bios from v606 to v803 before new cpu, ran fine with new bios. carefully swapped cpus, powered up, heard one beep got asus mobo screen (press del for setup, tab for bios...that screen) but doesnt go farther than that. doesnt respond to del or tab or any key for that matter at that point, and only stays at that screen for a few seconds before going to black, beeping once, and going back to asus mobo screen. rinse and repeat. i put the old cpu back in and it boots fine. completely stumped any help is appreciated.
sorry lol forgot to update. basically, i figured out that when i use my core unlocker on the quad core (basically turning it into a six core) the mobo cant run six cores and shuts down, boots again, realizes its a six core again, shuts down, so-on so-forth. i managed to get to the setup screen though and reset the bios to default and left it as a quad core, boots fine now. thank you guys for your quick, helpful replys!