you have an asus mobo, did u update the chipset drivers in the past few months ?
did you double check ncq is disabled as new chipset drivers tends to reset it
also whats the event viewer like error wise ?
Asus P5K-E/Wifi
Not updated anything in a while tbh other than the GFX drivers.
Dont think NCQ is enabled..
Event Viewers not showing and ntfs/disk related errors.