Pressing and holding the disc eject key on the keyboard during startup does not work either? Try starting normally and immediately running Disk Utility to eject the disc. Try logging out to the login screen and pressing he disc eject key in the keyboard. FYI - You are posting in the iMac (CRT) category (for the old iMac G3).
Mac Can't Eject Disc
Can't Eject Cd From Imac If Stuck
Use any of the following methods to eject a CD or DVD when you’re using Windows on your Mac.
- Press and hold the Media Eject key ⏏ at the top of your Apple keyboard (on Mac computers with a DVD drive) until the eject symbol appears onscreen.
- Right-click the disc icon in Windows Explorer (Windows 7) or File Explorer (Windows 8 or later), then choose Eject.
- Select the disc icon in Windows Explorer, then click Eject.
- As your Mac is starting up, hold down the primary mouse or trackpad button until the disc is ejected.
- To open or close the second optical drive of a Mac Pro computer, press Option-Eject.
You can’t eject a disc when the Windows Welcome Screen is displayed. Log in to a user account, then try again.
If the Media Eject key doesn’t work, make sure you installed the Boot Camp drivers. The function keys on Apple keyboards work in Windows only after you install the latest Windows support software. For information about installing the Windows support software, see the Apple Support article If some Mac features don‘t work when running Windows in Boot Camp.
See alsoGet started with Boot Camp Control Panel on MacRight-click in Windows with Boot Camp on Mac