BlackRat, XP has no problem with this amount of memory. As JetII said, there may be a motherboard limitation.. .On the other hand, are your fans working? . .Very often the PSU fan does not start and it gets really egg-boiling hot inside the machine.. .. .I cannot highlight enough, with the CPUs running at 1 GHz and more, there is no need for any radiator in your room, the DVD-drive or CD-burner and the harddrives do the rest.. .I am in my company right now in the middle of a test-program and the results are stunning, even representatives of ASUS invited us for dinner after they saw the differences a well designed airflow and cooling set-up can give.. .. .We are testing a 2GHz P4 with 6 SCSI drives, 1.5 GB RAM on an ASUS board, a DVD-burner, a floppy drive and a 128 MB graphics adapter in a new machine. Soundproof cabinet with 15 (!!!!) individual fans, the machine beats whatever was brought in to compare, even with the same (!!!) equipment. While standard cabinets heat up easily to some 40 deg C, our one stayed at below 25 deg C.. .. .Chips, like the one on the RAMs, are due to fail above 70 deg C....