Actually main "memory problem's" are 90% of the time is caused by the hard drive. Many non-techs forget that the operating systems create swap files for ran, temp files, etc... and for example, even if you completely turn virtual memory off in windows, it still uses some 'minimal' swap files, (example photoshop is a great abuser of this,).
Often the easiest check that can be done, is to go into ones BIOS and turn off Quick boot, turn on full mem check, and/or however your bios sets up to check the memory prior to even running your operating system. If it passes this, then there is only about a 2% chance it is the actual ram.
If you note and do the math... 90% IS the hard drive, 2% is the ram... okay, the other area that is the other 8%? Your video card. Yup, it contains ram on it, and many systems actually share into that in more ways than just 'displaying video'.
Of course this is basically finite, as you could add in a lan card that is self bootable and has mem cache on it, etc... I've even viewed that to cause a memory problem once. But only the one time in over 20 years.
Good luck!