No. I would say that is not normal. Is WMP perhaps indexing files from an external drive? Mine did for about 12 hours and had very high CPU usage in the process. Does it still do this with all externals disconnected?
I HAVE THE SAME ISSUE! Disk is at 100% usage latency always 900-2000ms on the performance tab of task manager. On processes tab it only shows roughly 40% consistently high is still pretty high. Running on an I7 3630qm 8gb ram clean clean install as in the "extensive" format and reinstall of windows 8 from the settings General- remove everything and reinstall windows. Took roughly 8-10 hours. If it helps i am also unable to access bios without removing my primary HDD and pushing F2. This only started after i went back to win 7. Then went back to win 8. Both clean installs same issue on both causing bad lag and performance.