Can I install the windows 7 Pro EOM SOFTWARE on more than one PC

No. They each need their own license.

so I can't???

OEM software is licensed to the first MOBO it is installed on and stays with that system ( Only legal method to bring it to a new system is if the old MOBO dies and there is no equal replacement board available for purchase as a replacement ) Which is the main reason it is less costly than the Retail version which can be moved from system to system as long as it is being used on only 1 system at a time. -- You can use the installation media to install on more than 1 system but will need to purchase a new license for each system it is installed on after the 30 day trial period expires.