Have you installed the drivers? Try installing HTC Sync to install the drivers, once it is loaded and you tried it once, you can uninstall it, the drivers will stay.
I also have an older version of the driver pre-Sync. http://mypcdominion.com/Files/androi...r3.0.0.007.exe
It you have the drivers installed, try to reboot the phone into the bootloader and then plug the phone into the PC. Sometimes the PC doesn't make the transition from one "device"(ADB Device) to the next (Fastboot device).
Helpful Rezound Links:
Guide to Unlocking, Rooting, ROM'ing, and FAQ
Did you know: You can upgrade your Rezound to ICS without rooting?
Fun Rezound Fact: The antennas for the Rezound are in the battery cover.
Don't forget to backup your flash player install before they remove it from the Android Market.
If you don't understand something, ask questions.
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