Insatlling Ram

[!Temjin!]

hello yall. i have a litl problem here mabe some one might have some info that can help me.
my ps consist of the folowing parts

abit kd7a mb
amd 2600 cpu
western 40gig hd
sony dvd-rw
ati 9800xt
256 mushkin pc400 blue ram
350 power supply

my litl problem is that i have just bought another stick of mushkin 256 ram. so that i can have 512.
if i put in the second stick of ram in the sys it will give me the blue screen when trying to load winxp.
i took out the new stick and the sys loaded fine.
i then put only just the new stick of ram in and booted up the sys. and it was working fine.
i put in both sticks of ram again and the sys wuld do 3 difrent things.
1. go to blue scree with memory not readable then reboot.
2.hang on post.
3.change the speed of the ram.
when the sys changed the speed of ram to 333 it loaded os fine but a bit slow. i went in to bios and all setings are at defaults.
i tryed the ram in difrent banks also but that did not change eanyting. i also put in both sticks of ram in slots 1 and 2 and reset the bios. when it came back up it loaded os fine but then went to a blue screen and shut off. both sticks of ram are good.
is ther a seting in bios that i might have to change ?
i havent updated the bios yet becoz i have herd that it can couse some harm to the sys.

whell that my litl problem people. can eany one help ????

[Azn_tweaker]

maybe u bought the wrong RAM. or ur motherboard dosent support that RAM.. also check if u put it in right.