how does the computer run with out hard disk.

turn it on ,it wshould run all day ,you just won't be able to do anything with it as it need an operating system install on a harddrive to be used .
you could try downloading linux live cd in my signature ,burn it to disk ,and boot computer to it ,it runs from cdrom and used ram for some file storage ,BUT! it may not work as it sometime looks for a hardrive

If you're just curious as to whether it's possible, you've got your answer. However, it's not worth the time or money to do it.

what time what money ,time is free and so is the download !