Directly after POST (Power On Self Test - the screen with the energy
star logo) the screen blanks, then displays a message like "Searching
devices" with a rotating slash and does so for up to 30 seconds.
This is the ATA100 onboard controller BIOS which searches for devices.
If you don't want to boot from a device attached to the ATA100 controller,
disable the BIOS. This will still let you use all devices which are
attached, but booting will be faster.
When using 1004a or later Bios : In Setup go to "Boot Menu"
and set the option "Load onboard ATA Bios" (or something similar,
anyway) to disabled.
1003 and older doesn't have this Option. But you can use a modified
1003 with the ATA100 BIOS removed. Look here