You would run fastboot devices to check and see that fastboot mode is working. Are you sure you're in fastboot not regular bootloader? See what fastboot devices gets you, you need to have the bootloader in fastboot USB mode for it where adb devices works with the rom booted or in bootloader I believe.
Sent from my DNA... S-Off like a baws
---------- Post added at 07:31 PM ---------- Previous post was at 07:28 PM ----------
I'm running windows 8 by the way and I've already rooted and S-OFFed my phone if that makes a difference. Also, I made sure to plug my phone in a USB 2.0 port.