Did you try 1 stick in slot 0 by itself? Usually the slots are numbered. You may need to insert them into slots 0 and 2, skipping one slot. But I would try the single one first in slot 0. Is your memory unbuffered non-ECC? I'm having spontaneous reboots with an hp machine as well as other errors, but I'm using 1 gb DDR. Everything was fine until I added the 1 gb chip to the 3 x 512mb already installed. Specs from HP for your motherboard: * Dual-channel memory architecture * 4 x 240-pin DIMM sockets support unbuffered non-ECC 4 GB 533/400 MHZ DDR2 memory modules * Maximum HP/Compaq approved memory is 4 GB* Mark Lundy wrote: > I have an HP a1020n P4 3Ghz with 2 256Mb of DDR2/3200 PC2-333 sticks in it. > I replaced those with 2 1Gb DDR2/3200 PC2-533/400 sticks. The BIOS sees the > 2Gb. However, WinXP Home hangs during bootup, always at the point when the > blue bars are moving across mid-screen. WinXP will bootup in safe mode and > it does see the 2Gb of RAM. > I have made sure the BIOS is the latest version. I have installed only one > stick at a time. I have put the sticks in the other pair of slots on the > MB. WinXp always hangs during the same time at bootup! > Hope someone has some ideas. Thanks in advance. > Mark The NOSPIN Group is now offering Free PC Tech support at our newest website: http://freepctech.com