After having used the VM for several days, I decided to restart the VM so that I can do some performance bench marking with minimal processes running. The VM did come up but I am no longer able to access it through Putty or browser based SSH. The private/public keys are all in place and they are the same ones that were used to get access before.
I get the following error when using the Google provided browser based SSH window..
Connection Failed We are unable to connect to the VM on port 22. Learn more about possible causes of this issue.
My colleagues who used to have access to the same machines are also not able to access it anymore. So my client machine isn't the problem. The VM instances dashboard says the instance is running.
Any thoughts on what could have gone wrong and how to debug this? The log files that I can access from the VM instances dashboard don't indicate any errors.