Sounds more like a HDD issue to me. Still, best way to go about it is to run some diagnostic software. What brand is the HDD? Usually all major brands have diagnostic software that can tell you whether the HDD is bad or not.
Also, download and run Memtest86+ for several hours, testing one stick of RAM at a time. If there are any errors that come back, then that stick is likely bad.
If it is the HDD, keep in mind that even brand new HDDs can fail, so the seller may have unknowingly sold you a bad HDD.