Command prompt isn't real DOS since it exists within a window. Getting into pure DOS requires a bootable floppy or CD-ROM, which doesn't load up the drivers for Windows. I was suggesting trying to "recover" the drive through pure DOS first. Then next time you want to try other firmwares, you can use Binflash. WXP allows you to create a bootable floppy, granted you have a FDD, otherwise, you can create a bootable CD. Check here for more information.
If you go with the floppy route, use one diskette for booting, and another diskette having the nec2x00a flasher and .bin file, which you can copy through Windows first.
Unfortunately, the ND2x00A series of drives aren't great readers, but excellent burners. It usually takes a while for the disc to spin up and get recognized.
If you go to device manager, is the drive recognized under DVD/CD-ROM drives folder when you expand it?