Check the reachability of the server via Ping and SSH.
If the server is still not responding:
Perform a server reset with the following manual: Perform a server reset.
If you still (after approx. 10 – 15 minutes) have no access to the server:
Start the rescue system with this manual: Start the rescue system.
If the problem persists:
Start the vKVM rescue system, using this manual: Using the vKVM.
If you have checked all points and the problem still exists, please contact our support under firstname.lastname@example.org and describe the problem in detail and the steps you already proceeded, so that we can initiate a hardware exchange, if neccessary.