Due to some technical difficulties on the AWS side, sometimes it happens that some customers are not able not to create instances in some of the regions. Please ignore that for now as it is the common issue for the free tier account. You can try using the ssh or putty after sometime and it will work fine.
There could be other problems as you might not have used the default vpc.
If you are using non-default VPC then you might not have attached Internet Gateway with your subnet.
These could be the probable reasons.