I had the same problem and I did the same actions like you,and the result was the same.But I used safe mode and HDD usage was very low ,so I thought that I had some programs that were increasing HDD performance and that's why I turned off my antivirus-kaspersky internet security 2013 and I get very good result,my laptop was working very quickly [sorry for my english]A week ago I did a completely fresh install of Windows 8 64 bit and everything was working great. When I booted up my laptop on Wednesday I noticed it was running terribly slow. When I opened task manager I saw that disk usage was at 100% despite the combined total of data transfer being 0.8MB/s.
The problem occurs constantly if I set my laptop power mode to balanced but only occurs intermittently at high performance. I've run a chkdsk and everything is showing up fine and bizarrely there is no slowdown whatsoever on safe mode.
Any idea what I may have done wrong?