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

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