The massive flooding in Thailand put the HDD market in a very rough spot late last year. The flooding meant that plants in Thailand that make HDDs were unable to produce HDDs and production in some instances had to be shifted to other countries. The reduced output meant shortages and increasing prices for computer makers.
The computer industry is very closely related so a shortage in one component means that fewer computers ship. With fewer computers shipping, less related components that are used in the ecosystem ship. This is why NVIDIA is pointing to the HDD shortage as one reason its quarterly financials are down. The fact that HDD shortages meant fewer computers shipped meant that less of its GPUs shipped.
Lower GPU shipments aren't the only cause of earnings being down at NVIDIA. The company also notes that shipment of Tegra 2 chips for mobile devices were down. The Tegra 3 processors that replaced the Tegra 2 are ramping up in production. NVIDIA posted earnings of $950 million and was expected to post $1.066 billion. AMD pointed to the same HDD shortage as a reason for reduced shipments of its hardware, so NVIDIA isn't alone.