It sounds like you generalized a VM and afterwards are unable to start the original VM is that correct?
This information can be found on the documentation page. After you have run Sysprep on a VM, that VM is considered generalized and cannot be restarted. The process of generalizing a VM is not reversible. If you need to keep the original VM functioning, you should create a copy of the VM and generalize its copy. You should be able to launch new VMs from this image that was created.
If the sysprep is not run inside the server and captured from the portal - You can recover the VM by taking a snapshot of the OS disk - Create a disk with it and deploy a VM. More information and steps can be found here.
Hope this resolves your issues. Let me know if you need additional help or have further questions.
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