The operating system resides on the hard disk - it is usually put on at the factory - if you take out the original hard disk you then need to rebuild the OS on any new disk.
To do this you need the OS media on a CD and a CD drive to read it - and the Product Authorisation Key - a number on the media package and sometimes on a sticker on the machine itself.
You need to set the machine's BIOS boot-priority to CD rather than Hard Disk.
After building the OS on the new disk you then need to change the boot priority again - back to hard disk.
Your machine's BIOS is trying to find a Boot Sector (with software) on the hard disk - it's not there until you put it on. You have no bootable device - as per the screen message.
Peccavi, January 2010
