Z77A-GD65, "Missing Operating System" after running Live Update

So here's the brand new computer I assembled:

$309.99 HIS IceQ Boost Clock H795QC3G2M Radeon HD 7950 3GB 384-bit GDDR5 PCI Express 3.0 x16
$219.99 Intel Core i5-3570K Ivy Bridge 3.4GHz (3.8GHz Turbo) LGA 1155 77W Quad-Core Processor Intel HD Graphics 4...