Overclocking the K7T266 Pro passed 137FSB has been known to cause USB to intermittently drop or fail completely. Until recently this issue has been blamed on MSI putting out a faulty board and the K7T266 community has been hoping and waiting for a BIOS update to fix it.
As of recently, other boards based on the VIA KT266 Chipset have emerged, like the Epox 8KHA and Shuttle AK31, and we are now hearing that these boards as well have issues with USB passed 137FSB!
It appears the VIA KT266 Chipset is at fault. For more information please refer to the Forum in these threads here or here