Download H.2 from MSI: http://www.msi.com/support/mb/X99S-GAMING-7.html#down-bios
Decompress the archive and put the bios file (E7885IMS.H20) on a FAT formatted USB stick. Start the system with the stick connected.
If you know the version bios a was at...
Decompress the archive and put the bios file (E7885IMS.H20) on a FAT formatted USB stick. Start the system with the stick connected.
If you know the version bios a was at...