Without more information I am going to assume this is a RAM issue. You have 8gb of RAM but you don't actually have 8gb because your OS (I am going to assume windows) you only have roughly 4gb (+or - 1gb) to play with. You may be skirting by on the 8gb but closing the game or doing literally anything else to increase your RAM usage will BSOD your system. Try giving at least 12 and seeing if that improves anything.
Also If your computer image is old I would suggest blowing it out and starting fresh. IE reimage your system. Don't factory restore it. This will generally just improve performance.