What OS is on the pendrive that you are attempting to boot to? Commonly older boards should be able to at least boot to DOS on a pendrive. Have you loaded BIOS default values and saved out of there? I don't recall the specifics but on the boot related sections of some BIOS setup pages, there are more than one option associated with bootable USB devices and of course the USB pendrive will need to be first or the PC will boot from whatever else is first in the boot order.
You could also check that you have the latest BIOS installed for your board and read the file detailing the history of fixes included with newer BIOS versions (often on Intels BIOS download page) if its not already the latest - perhaps the newest version includes fixes for your specific problem?