Dell Inspiron 660s W7 Home Premium Svc. pk. 1, 64 Bit. Used, OS was replaced. Runs fine for awhile then, at random, will power off and immediately restart. sometimes it will go a day or two with no issue, then off/on after 5 minutes of use, last week it did the off/on 4 times 14 minutes apart. 1 month ago it would flash error black screen, but would not respond, just looped. Got it to safe-mode and booted normally. It now boots normally after on/off, but there does not seem to be any specific cause for the issue. Thank you.