I have a MSI K8MM3-V AMD x64 motherboard with 2GB's of RAM, an AMD Athlon 64 3200Mhz processor. a 256 MB NVidia AGP video card, a Creative sound card and a Coolmax 550 watt power supply. I run Vista Home Basic x64 on it.

I just recently put in the motherboard, which is refurbished. At first, when I would go into standby mode or sleep, the unit would shut down and the power LED light would blink on and off until I resumed it from standby. Now, all of sudden, it has stopped blinking when I put it to sleep. I know it's not the LED because it always shows green when it's in normal operations. What went wrong?

You said that your MB is refurbished. Perhaps it is slowly malfunctioning. How old is it? Also the wires for the LED might be loose or Vista really isn't putting it into sleep mode otherwise I have no clue (sorry). If it works fine otherwise then it could just another unexplained glitch that frequent computer systems.