This document describes the possible causes of Windows instance login failures and their troubleshooting methods. You can follow the instructions to identify the cause of your problem and learn how to fix it.
Failure to log into a Windows instance may be the result of:
If you cannot troubleshoot with a diagnosis tool, we recommend that you log in through VNC and follow the instructions on the CVM.
If you cannot log in to a Windows instance through RDP or remote access software, you can log in through VNC instead, which helps you identify the cause of the problem.
If you forget the password for the instance, you can reset it in the console. For more information, see Resetting the Instance Password.
Problem: the login attempt failed because you forgot the password, entered an incorrect password, or failed to reset your password.
Procedure: reset the password for this instance in the CVM Console and restart the instance. For more information, see Resetting Instance Password.
Problem: Cloud Monitor shows a high load on the server’s CPU, and the system cannot be accessed remotely or access is slow.
Possible cause: viruses, trojans, third-party antivirus software, application exceptions, driver exceptions, and automatic updates of software on the backend may lead to high CPU utilization, causing CVM login failures or slow access.
Problem: the remote access attempt to an instance failed, the remote access port is not the default port or has been modified, or port 3389 is not open.
Diagnosis: ping the public IP address of the instance to check network connectivity and run telnet to check whether the port is open.
Procedure: See [Remote Login Failure Due to Port Issues] (https://intl.cloud.tencent.com/document/product/213/32540) for the detailed procedure.
Procedure: Troubleshoot with the security group (port) verification tool.
For a remotely logged-in Windows instance, you need to open port 3389.
If the problem is caused by a port issue of the security group, you can use the Open all ports function to open all ports.
To define a custom rule for the security group, see Adding Rules for a Security Group.
Problem: the login attempt failed due to the CVM firewall or security software.
Diagnosis: log in to a Windows instance through VNC to check whether the firewall is enabled and whether security software such as 360 Total Security or security dongles are installed on the server.
This operation involves shutting down the CVM firewall. To perform it, check that you have the corresponding permission.
Procedure: shut down the firewall or the installed security software, and then try to access remotely again. For example, you can shut down the firewall of Windows Server 2016 as follows:
Problem: when you tried to log in to a Windows instance through the remote desktop, the prompt stating "Authentication error. Invalid flag is provided to the function." or "Authentication error. The required function is not supported." appears.
Possible cause: Microsoft released a security update in March 2018. This update fixes a remote code execution vulnerability in the Credential Security Supporting Program (CredSSP) by correcting how CredSSP validates requests during the authentication process. Both the client and server need to be updated or the preceding error may occur.
Procedure: install the security update (recommended). For details, see An Authentication Error Occurred when You Tried to Log In to a Windows Instance Remotely.
After trying the preceding methods, if you still cannot log in to the Window instance, please save your self-diagnosis results and submit a ticket for assistance.