I find it absurd: from Google 0 support, no phone support, no email support and no chat support. Even if mine is a free trial, there should be a minimum of minimum support, or not?
However, I hope to find a solution here:
After creating a Windows Virtual Machine on Google Cloud Platform I tried to connect with it via the RDP (Remote Desktop Connection) app. It always replies that the password is incorrect, even though I am 100% sure that the password is correct. I tried with the login credentials created with the VM, and it doesn't work, then I tried with the login credentials of my old Microsoft Account and that also doesn't work. Finally, in order not to miss anything, I also tried those from Google ... but nothing!
Of course in the Firewall I checked the box to allow RDP to access TCP Port 3389 and then I updated the VM
As mentioned in the comments, it may take some minutes for Windows VMs to be ready. After the VM has finished booting, which may take a few minutes, you could confirm its state using one of the following methods. By using Serial port 1, Serial port 2 or VM screenshot you will ensure the services up and running correctly.
Each Compute Engine Windows instance must have a local password set if it is not already on a domain or custom image. Once you have confirmed the services, you can check your Windows instance password by connecting to the VM through the Google Cloud CLI command-line tool or Cloud Console.
If you still have issues connecting, try creating or resetting the password