> Tested each memory module in DDR1 slot for at least 20 > hours. > > Tested each slot with the 512MB module for another 20 hours. > Should I have used the 1GB module for this? So it appears that each memory module works fine if it's the only module installed - in whatever slot. I found this helpfull guide for using Memtest86+: http://www.overclockers.com/forums/showthread.php?t=409152 Memtest86+ website: http://www.memtest.org/ Memtest86+ Forum: http://forum.canardpc.com/forumdisplay.php?f=73 Cannot find a mailing list though. My machine has been known to freeze on occassions, which I put down to software issues while running Fedora. The 2 1GB memory modules are 1 low density and 1 high density. Both are PC2100. They work fine on their own, but don't want to work together. I'm now running Memtest no. 5 using the 1GB low density module, and the 512MB module, which is also low density. I have put a digital multimeter on the power supply, and overnight while testing it registers ~ 4.97 - 4.98 volts on the 5vdc line, with a stable reading. ie it changes slowly between those 2 values. So it looks like the PSU is fine. I have a sneaking suspicion that it's the mismatched low and high density memory modules that are the problem? Kind Regards, Keith Roberts