New ram problem :(

I recently bought a 1 gig ram stick (from newegg) to add to my pc, which already had 2x512 but since I've installed this new ram I've been having random lock-ups where the pc can only be recovered by turning it off and back on.

The ram (x2 512/1GIG) is both the same brand PQI DDR-400 PC3200 so there shouldn't be any conflict. I've also done a memory (memtest86) test which found no errors so all I can think of is there are issues where the ram is placed?

My motherboard is Aopen AX4SP-N and the ram slots have;

[BLUE] [PURPLE] [BLUE] [PURPLE]
512--------1gig------------512-------blank
http://img63.imageshack.us/my.php?image=untitledch8.jpg

Now I've tried other placements but I'm still randomly locking up. It happens MAINLY when I'm playing games (wow/cod2). But happened once while I was using nero. It usually happens 1-2 hours after gaming or sometimes right as soon as I boot up (but rarely).

I also just put in a 450W power-supply and a new DVD/CD-RW so maybe this might have something to do with it.

Anyone have any info on what I can do to fix this, maybe I need to edit BIOS or something in windows?

Any help would be awesome, thanks in advance. -Mark

WIN-XP PRO fully updated
2.40GHz
Motherboard - AX4SP-N

 

I would say that you are now running in single channel mode, as you are only using three slots- you need to be using 2, or, 4 same colour slots to run dual channel, - try removing the 1gb stick, and see if it locks up. You will be running dual channel with 2 x 512 sticks in slots 1, and 3, and this will probably make the difference , icreasing your fsb to 800, whereas 3 sticks= single channel- runs at fsb 400.

 

See page 37 in your manual.
http://download.aopen.com.tw/Default_prod.aspx