Personally speaking - boxes shouldn't reboot except occasionally and even then, overnight.
If yours is doing it in any other circumstance, there's probably a fault somewhere which VM will need to rectify. Potentially, your box needs replacing.
You can either wait on here for VM staff (may be a day or so) or call into faults on 150 (from a VM phone) or 0345 4541111 (from any other phone)
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