Perhaps someone here knows the answer, it sure has me scratching my head. My wife's computer is a HP m9515y that came with 8 gigs of PC -6400 ram. 2 gig sticks in each slot. Worked fine for two years. About 2 months ago, it would randomly hang or not come out of low power state after sitting for a couple of hours. We normally turn off computers during the week, but let them on from Fri. night to Sunday night. This wasn't an everytime thing, it might work fine for weeks, then hang. A power switch shutdown and reboot always worked and brought it back. This morning, different story. She checked email and we went out for 30 minutes, came back and the screen is up but won't do anything. Shut it down, will power up the fans but no boot, won't even go through bios screen. I thought it might be HD, put the latest clone in, no go, still nothing. Removed the second pair of memory sticks, it booted like nothing wrong. Put current HD back in, still OK. Take out first pair of memory sticks, insert in 3rd & 4th slots, boots fine again. Insert pair of memory that were originally in slots 3 & 4 into slot 1 & 2 with 3 & 4 empty, again, fine nothing wrong. So this now seems to tell me that all four sticks are OK and all 4 slots are OK, BUT put the 4 sticks back in, same problem, won't boot. It's weird, any two sticks will work in either pair of slots, but not 4 sticks in 4 slots. Any ideas???