A few things that might help if you try them...
- Try the online scanners like Kaspersky or Panda. They may help identify an infection.
- Run Memtest86+ to test your RAM. D/load link on my sig.
- Run an HDD diagnostic like Hitachi Drive Fitness Test (if you are using Hitachi/IBM drives). D/load link on my sig. Get the one for your HDD brand.