If you have tested your Memory and you are certain you do not have an HDD issue. I would try to repair windows 7, If this also fails i would format and reinstall to eliminate your Win7 as the culprit.
**Always save your info on an external drive. ALWAYS!
This way if you get a virus or destroy your HDD doing whatever you can easily reinstall and be on your way quickly. I have an image of my machine, and store everything externally. When I run into issues such as yours I don’t even bother trying to resolve it… just format and install image, im back up in the hour.