I have a system with 2 sticks of DDR400 RAM, each 512MB. When I run it with only one stick (either one!) installed, it runs fine for weeks. When I run it with both installed, Windows blue-screens within a day. What gives? Any idea what could be causing this? The box ran just fine for months with both sticks installed, then a couple of months ago it started to blue screen. So I tested it with just one stick (no problems) then just the other (no problems) and then both again (problems). I tried swapping the position of the two sticks, but it still crashed. I posted here about this a few weeks ago, when I thought the problem might be due to a my installation of Windows. But that doesn't seem likely to me now, since it runs just fine with only 512MB installed. I also ran memtest overnight with both sticks installed and found no problems. BTW the RAM modules are identical. My system specs: - Asus A8V mobo with Via K8T800 Pro - 1GB (2 x 512) DDR400 RAM - Athlon XP 3000+ cpu - ATI Radeon 9600XT videocard - onboard audio (Realtek AC97) - Windows XP Professional SP2 (fully patched) - Boot drive is a partition on a 120GB Western Digital drive running as Master on the 1st IDE channel (a second 120GB WD drive is the slave on this channel) - 2nd IDE channel master and slave are a Lite-On DVD-ROM drive and a TDK CD-RW burner - On-board RAID controller running two SATA 320GB WD drives in RAID 1 (mirror) - Westell DSL modem - 500 watt Antec SmartPower 2.0 psu I am wondering if it could be a mobo problem? Something wrong with the second RAM slot? Or could Windows somehow have a problem with 1GB but not 512MB? (A problem it only recently developed?) I'd love to avoid either buying unnecessary replacement parts or re-installing Windows from scratch if I can avoid either. Maybe I should try running another OS (I have another partition with Linux on it) with both sticks installed to see if it crashes again? Or set up a new blank partition and install WinXP to it as a test? Thanks.