AWS can not start instance Error: Instance does not have a volume attached at root (/dev/sda1)

 This is because your volume is detached

In AWS console,

go to your volume, 

select actions -> attach volume, select instance Id, then 

for the drive select what ever the message is saying in this case,

/dev/sda1

https://stackoverflow.com/questions/37142357/error-instance-does-not-have-a-volume-attached-at-root-dev-sda1