After installation Hyper-V role on the Windows Server it reboots cycling.

If you face the issue - after installation Hyper-V role on the Windows Server it reboots cycling, you need to try advice below.

I faced with it on server HP DL380p Gen 8 with OS Windows Server 2019.

So, you should do next steps:

1. Need to go to the BIOS, in my case I restarted server and push button F9 to enter to BIOS. 

2. Then you need to find sittings of processors and disable VT-d.

3. After save changes and reboot server.

4. Server should start correct, when Hyper-V role will be installed fully you can enable VT-d again and server will work correctly.

PS. Find this advice here - https://serverfault.com/questions/937402/windows-server-2019-fails-after-hyper-v-role-install