Firstly, please make sure that your PC meets the The Witcher 3: Wild Hunt system requirements.
If the requirements are met please make sure that all applications non essential for your pc are turned off/disabled. This includes antivirus/antimalware programs.
If that won't help please check if your PC is malware/virus free - those may sometimes cause crashes.
You may also try verifying game files, as described here.
If any of the above won't help, reinstall your GPU drivers. To do so completely follow these steps:
Please be aware that sometimes installing older drivers might help with crashing.