Here is an interest issue. Computer is running like a dog. You have run defrag, Check Disk, remove all non required application, maybe even rebuild the computer with a freash install, and still it runs like a dog.
What could be happen is that Windows could have placed your HDD in PIO only Mode. This will dramatically reduce your HDD access speed.
If you run Bench32 on the disk you find that it is only access the drive at about 10% of the drive speed. EG.-