DDR333 is relatively old, I wouldn't be surprised if you lost some hardware due to age. Use the process of elimination to determine the cause by removing parts you don't need to POST, such as HDD, all but one stick of RAM, CD, any cards you have plugged in to PCI slots, and try booting. If it goes past the POST screen (it won't boot because there is no HDD plugged in), then you've eliminated the cause. Now, plug in each piece one at a time and attempt a boot after each piece is installed. Once you plug in the piece that fails, you've found the problem.