Check if other HP Pavilion 1000 series computers use a dual core, and verify if they use the same MB. You might be able to find the BIOS for another HP computer with a dual core using the same mobo.
Otherwise contact them via IM service line.
If the BIOS is not compatible with this MB, the flash might render the motherboard useless.
You might want to try contacting MSI, too.
Good luck!