I recently installed D5 Render version 2.6.1.0423. When I open the D5 my PC get restarted automatically.

D5 1

Hello, did you encounter a dll error? If so, could you show me a screenshot of the error?
If it’s not a dll error, I suggest you upgrade your driver to the latest version. If this still doesn’t help, please send me your logs. This post shows how to collect logs. D5 Support Tool - Get Help / Tech Support - D5 RENDER FORUM
You can share a link here or send your log to our email. (support@d5techs.com, please describe the problem and attach the link of this post to your mail)