What is brand and model of computer?
It is actually less costly for that model, to replace the cpu and motherboard together for that old, old unit... You can actually get a used computer that works well for less than it would cost you to fix that Duron.
Whatever you do, you will have trouble with Windows, as it will detect a change in hardware and refuse to cooperate until you run a repair install.
Do you have proprietary software, such as a Windows version for a specific brand?