If your computer boots up, goes through the POST and the displays that the operating system is not found, I doubt very much that it is strictly your motherboard. Yes, this particular computer series has issues with overheating and bad GPU (Video Chip) but none on those would cause your symptom. It sounds to me like you lost your operating system. I suppose you were running Windows on your computer. I would most certainly try to boot from your CD and see if you can reinstall it. A bad Hard drive (cheaper and easier to replace) can also be the cause of this. Hope I make sense. Let me know if I can clarify this for you....:-) good Luck