Exact same problem with a GEForce6100sm-m ECS motherboard, 4 years old. Worked ok for a few years with Vista home premium. Recently shuts down without any warning, whether booting to normal Vista OS, or booting to Puppy linux on USK memory stick. Ruled out PSU, memory, any cards, or devices, down to either the motherboard od the AMD proc. Will give memory beeps if dimms removed, and will not shut down if left in the BIOS. Does anyone know if there is some fault with this board, or does it fail after a period, or could it be the proc???
Cpus rarely fail, unless the heatsink broke off or the heatsink fan has stopped turning for an extended time. Computer geeks has some older boards and combos. Pricewatch may also find a vender with your board chipsett. It's common, but many are so old that they won't work and are sold as is on ebay. My best recommendation is to change the cpu and board together; if the cost of old tech (used) is the same as new, then change to ddr3 ram; if your power supply is over 2 years old, then change it also to antec, corsair, or ocz. Oem power supplies for dell and hp aren't designed to last.