The eject button on my cd / dvd drive is broken.
I can still eject using windows explorer from the context menu.
I need to reinstall windows.
Is there a function key combination i can use from the boot up screen ?
You can always stick a fine allen key or unfolded paper clip into the little hole (usually just under the tray):
This image is apparently of the Inspiron DVD drive and you can see the hole on the right next to the button:
Eject the CD from your current install of Windows, place Windows re-install CD in drive, close, reboot, and install Windows. Windows will go through its install basic stuff, reboot, finish Windows install, and then boot up into a fresh copy of Windows. From there, you can eject the Windows CD from the new Windows.