I was trying to install the factory software image from https://developers.google.com/android/images#blueline on my Pixel 3. I downloaded the image as well as the platform-tools with adb and fastboot.
After plugging in my phone, I ran
adb reboot bootloader which put me into Fastboot mode. After this I tried to run the flash-all.bat file, but it was just stuck on the "waiting for devices" prompt. I'm not sure what I did at this point, but I must have really messed up the phone, because now I can't even boot from Fastboot, where clicking "Start" just puts me back in fastboot with the reason "no valid slot to boot." Any idea how I can get my phone working again?