You could probably use the interactive serial console to connect to the Special Administrative Console (SAC) of your Windows instance. You can use the SAC to troubleshoot a Windows instance if you can't connect to it via Remote Desktop.
Before you connect, make sure you have created a Windows instance password and have it ready.
To connect to your Windows instance using an interactive serial console through the GCP Console, do the following:
Open the VM instances page in GCP Console and click the name of your instance. The VM instance details page opens.
Click Edit. Under Remote access, select Enable connecting to serial ports. This enables the interactive serial console for this instance.
Click Save, then return to the top of the page.
Under Remote access, click the drop-down list next to Connect to serial console, and select Serial port 2. A Windows Special Administrative Console (SAC) opens.
At the SAC> prompt, run cmd to create a new channel. SAC returns the channel name, for example, Cmd001.
Run ch -sn [CHANNEL_NAME] and press any key to connect to the channel. For example:
The Command Prompt session was successfully launched.
EVENT: A new channel has been created. Use "ch -?" for channel help.
SAC> ch -sn cmd0001
Press any key to confirm connection to the channel.
Enter the username, domain, and password of the instance to connect.