I have an Aspire z5101 all-in-one. It came with 2x2G of RAM and I added 2x2G more. Thing worked fine for a while, then I started getting BSODs - always followed by the machine not booting (powers on, the blue front LEDs come on, but it never gets to the POST screen). Unlugging for a few hours gets it booting again, but only until the next BSOD (sometimes hours, sometimes weeks).
Eventually, I relaized this is a memory issue, so I started troubleshooting.
If I remove all but 1 stick of RAM, things work perfectly. Any 1 of the 4 sticks I have work perfect, as long as I have it in slot 1 (or maybe it's 4, I don't know which side to count from). But as soon as I add a 2nd stick (I add the matching stick, and put it in the matching colour slot), the BSODs come back (usually within minutes). If I do a memtest, it runs for a bit, then I get a screen full of "snow" (colours dots everywhere). Same thing happens if I have 1 stick in any other slot.
So for now, I'm running with just the 1 stick of RAM, but running Windows 8.1 with 2G RAM isn't ideal.
So, I'm pretty sure all 4 sticks are good. Could it be that all 3 of my 4 DIMM slots are suddenly bad? Any suggestions would be greatly appricited.