Unable to reactivate 90 days free license on the same machine which was crashed earlier

The key can be reactivated in the same VE instance only. If you recreated, copied or moved VE instance then you are not able to reactivate the key any more. this is considered as a different box from key point of view. If the key is not expired yet, you need to call support for ability to activate the key on new instance.

No one can tell you the key difference but support team

A key does not linked to the version. It linked to the machine. You can install any version if the key is not expired and if your hardware/ve meets minimum system requirements for the version you are going to use.

For VE editions however. the latest version you can go with depends on license type. You need to contact support team to get information about your license limits.