Hi,
Checking the processes on your system indicates Windows is indexing. That process will slow the system somewhat until complete.
Windows desktop management is also running and error reporting is active.
Give the system some time to stabilize.
Any clanking sounds from system? You ran all tests and they have passed so the HD should be OK. However unusual clanking and constant disk activity could indicate an impending problem with the disk. Again, see what happens after indexing is complete.
BTW, I had the same problem with an HP factory drive (Hitachi). Replaced the drive (Seagate) and the symptoms wre corrected. The Hitachi drive became noisy and exhibited constant disk reads and unusual memory activity for no apparent reason.
Jaco