Why can I not RDP into my Windows EC2

I use the format ".\Administrator" (be sure to include the period) when I want to authenticate as the local Administrator user of the instance. If that still doesn't work and you are familiar with the AWS SSM service, you could attempt to connect to the instance via the SSM Session Manager component, which would give you a PowerShell session. There, you can create a new local administrator account by issuing the following commands:

1. net user <NEW_USER_NAME> <PASSWORD> /add
2. net localgroup administrators <NEW_USER_NAME> /add

For more information about how to setup SSM Session Manager, please take a look at the following link https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-getting-started.html

Try using this format, internal ip\administrator (example 192.168.0.1\administrator) as the username.

Also it sounds like the networking is correct if you can telnet, but just for reference this is how public and private subnets work within your VPC: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Scenario2.html If you do not have a subnet with a proper route to an IGW you will not be able to RDP in from the internet. Make sure the Route table(s) are setup with the correct 0.0.0.0/0 routes.

I assume the instance has been up for a while now, but also as an FYI a t2.micro Windows Server 2019 will take some time before it will be ready to receive inbound RDP connections after boot up.