|USB is part of the acpi power specification but you may or may not have it enabled in bios and with software. It may not be part of your bios or boards design. You'd have to look that up.|
Can I assume you mean that your power goes off and you want it to stay on? If so you may be forced to use a powered hub to keep the modem alive. It still may be that the drivers are faulty and won't resume.
Check bios settings first for any advanced power features and then to the OS for power settings.
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