If you have enabled caching on your HDD in the device manager and defragged your HDD, you may need to try to clone the drive. Look at Macrum Reflect for home or Clonezilla in order to clone the drive. Taking this action may help/save you before the drive fails.
Of course you will optimize your drive, load drivers including chipset drivers or RST for Intel if it applies. You should look at programs along with malware/viruses that may be slowing your drive down. If everything is clean and drivers are loaded, this poor performance may indicate a failing HDD.
We recently had a server slowing down. Drivers were loaded correctly, no malware, drive cache was enabled, startup programs were minimal and the transfer rate was below 50 mbps with HDDTune (free).
After trying to clone with software and using a Kanguru to try to clone the drive, these solutions failed- This is RARE. So what should you be ready to do? Create backups of your programs and files (including your profile) and get ready to install Windows and your programs on a new HDD.
Remember, if your HDD is rated at 7200 rpm or more and has good cache on board, you may have a drive that is failing even though SMART in the BIOS is enabled.
See our other article on how it could be your network card and not your HDD.