Do you have a RAID card by any chance? That's *exactly* how it would behave at boot time.
In the BIOS, make sure any "ROM" options (such as "Option ROM" or "PCI ROM") are set to disabled or try toggling their current state.
As designed, this is how the BIOS works: it first runs the POST to check present hardware and minimal functionality, it then has an option to run firmware from any installed PCI cards that need to initialize themselves prior to the system boot, and once control is returned back to the BIOS, it calls up the bootloader in the form of the MBR on disk 0 (or other selected disk).
A hang between BIOS and boot would be caused by either a) the BIOS looking for/trying to load the ROM from a PCI device to allow it to initialize, or b) the BIOS calling the initialization code in the add-on card, and that code taking time as it does its thing before returning control to the BIOS.
Failing that, your BIOS could need an update or your motherboard (one or more of its components, starting with EEPROM chip to the PCI buses) are on their way out.