I have an HP laptop, and I smashed the display, but I work on an external monitor. I want to reinstall Windows, but the external monitor works only if Windows is installed. What can I do?
Why does the external monitor only work if Windows is installed? That's not normal.
The notebook's video card should detect the presence of the external monitor and display on it automatically. There are two primary modes of operation for this: mirroring and expansion. The former simply mirrors the contents of the internal display onto the external display, which is useful for giving presentations to a large audience, or using your notebook after you've smashed the screen. The second option allows you to connect a second, external monitor to your notebook and use it in addition to the internal display, something that us multi-monitor enthusiasts can't live without.
Generally, the choice between those features is controlled with a special key combination on your notebook. Look for a Fn key and another key (generally one of the F-keys) that's labeled with something monitor-ish. Press those two keys together in order to toggle between the two video display modes. If everything goes well, you can put the machine into "video mirroring" mode, and see everything on the external screen that you would normally see on the internal screen.
(Yes, this answer is quite vague. You didn't give us any details about your notebook--what brand, what model, etc. I suggest checking your manual or the manufacturer's website for more details.)
You might try creating an unattended installation disk as suggested and using it on a blank hard drive. As long as the BIOS is set to load to the optical drive, you should be able to just put the disk in and let it go.
I would swap the hard drive with a blank one to protect the working OS from mishap. Most unattended installation disks will automatically partition and format the hard drive if it is empty.
The main problem is that without a display, you lose your ability to receive feedback from the computer. This forces you to use the machine as a normal computer tower.
Depending on what you are doing, you might be able to get a used/cheap workstation that is relatively small. It would allow you better flexibility and could be repaired much easier.
I had the same problem. I took my laptop apart and disconnected the LCD screen from the video card. This forced the display signal to use only the external monitor port. I was then able to install Windows Vista via the external monitor.