Have you checked in the computer for power saving settings? I've seen with some Dell laptops that the On-board NIC is switched off when wireless is being used to preserve the battery. Additionally the system BIOS can be strict on power saving and could be switching off the device but not resuming it when you need it to. Could also be Window's power settings which shouldn't really be doing anything, but it's worth a look. Other than power saving features, I wouldn't know off the top of my head other than to assume hardware trouble.