Official support for µVision 3 ended long before Windows 10 was released. Running it today comes with several known issues:
Installation steps (typical)
Here is how to obtain, install, and run uVision 3 on a modern Windows 10 system. keil uvision 3 download for windows 10
However, if you are maintaining a certified legacy system where the compiler version must remain identical to the original build, uVision 3 remains your best option. If you'd like, I can help you find: Official support for µVision 3 ended long before