If the CPU is the brains of your PC, the motherboard is the nerve centre connecting all the components. Even experienced upgraders may baulk at installing a motherboard, a process that often involves a complete overhaul of your PC. But there are compelling reasons for replacing the main system board.
For one, recent technologies – particularly the latest processors (including dual core), PCI Express graphics cards (including the latest dual card configurations), RAM and Sata (serial ATA) hard drives – are not supported by old boards. So if you want to use any of them, you'll almost certainly need to upgrade.