From the bug check codes page at Microsoft:
"Bug Check 0x9F: DRIVER_POWER_STATE_FAILURE
The DRIVER_POWER_STATE_FAILURE bug check has a value of 0x0000009F. This bug check indicates that the driver is in an inconsistent or invalid power state."
Update the major drivers in your system (video, sound and network, chipset). This bug check is generally caused by the network and chipset drivers, but update all 4 mentioned above to be sure.