I built my first computer yesterday. I did a lot of research into building my own PC before I purchased anything and I had some guidance from someone more knowledgeable than me. The computer was working fine yesterday, but I mistakenly put on Windows 7 32bit OS instead of 64bit so this morning I decided to reinstall the correct OS. It almost got to the end of the install when the computer switched off. Since then it hasn't worked - The machine wont turn on at all other than a green led on the motherboard . I opened it up and unplugged and replugged in everything in case something was loose. I saw a similar topic on this forum and attempted some of the suggestions on there too. Note: when I turn the power off and on at the wall and then try to start up the machine the processor fan spins once and a small red light on the motherboard flashs on once, though the manual doesn't indicate what that means. The Specs are: Coolermaster GX 750W PSU Asus M5A97 PRO 970 Socket AM3+ 8 Channel HD Audio ATX Motherboard AMD Phenom II X4 965 Black Edition 3.4GHz Socket AM3 6MB L3 Cache Cache 125W [w/ heat sink unit] 8GB GB (2x4GB) DDR3 2133MHz Any help or suggestions would be greatly appreciated. Thanks!