You don't eject the drive, even by accident, you only eject a disc, and that's something regular.

I'd reboot, and see if it reappears in Windows Explorer. If not, see if it is in Device Manager and if there is any yellow exclamation mark with it. If not even in Device Manager, boot into the BIOS setup and see if that mentions it, and if the boot sequence is set to 'optical drive first'). Then put a bootable disk in (like your Windows setup disk) and boot from that. Please tell your findings.

Kees