If you're unable to login to AWS EC2, then try to perform a system reboot.
1. Login to https://ap-southeast-1.console.aws.amazon.com/ec2/v2/home?region=ap-southeast-1#Instances:sort=instanceId
2. Click on "Action" > "Instance State" > "Reboot"
3. It will take a couple of minutes for system to reboot. Next you can login again using Remote Desktop Connection