Once it's open choose your main drive and click defragment. You should upgrade that RAM btw.. It's not a requirement to play RO or anything but it would really help your computer run faster. It is most likely that the computer is overheating. You should check the fans and vents to make sure they aren't blocked. If you're up for it, open it up (make sure it's off and unplugged) and with a handvac or some canned air clear the dust out.