AWS CLI in Windows EC2 cannot use role to access S3

Question

I am very new to AWS. I created an IAM role which has full access to S3. I assigned this role to a Windows Server EC2 instance. I then installed CLI on that instance. I then remoted into that instance using RDP, and started CMD windows, and typed in

aws s3 ls

It complained that

Unable to locate credentials. You can configure credentials by running "aws configure".

Now that this EC2 has been assigned the role that has full access to S3, why can't I directly access S3?

Answer 1

Loading the software in a fresh instance will solve the problem. Only if you know what is causing the instance to fail, we can solve it. But it is easier and faster to start with a new instance.