Ram issue

I recently bought more ram for my PC, I had 2 gigs before 2x1gig and i bought 2 512 sticks to populate the other 2 empty slots. But when i put the new ram in to bring my total to 3gigs my pc will not boot, as soon as i turn it on it beeps at me.
So I took the old ram out and just left the new stuff in and the pc booted fine. I have tried every possible combo of ram in the slots but nothing i do will let me boot with more than 2 gigs.
And yes, old ram and new ram are the same DDR400 (pc3200), and i know my mobo will support 4 gigs.

Im stumped on this one.

 

Oh btw i have
DFI Lanparty NF4 Sli
7800 gtx
300gig HD

 

What brand are the mem sticks and what are the latencies 2-2-2-5 ect.Often when mixing different brands and latencies you can run into problems,theres no way around it,some just dont like each other,try manually setting the latencies to the slowest of the rams and manually setting any ram tweaks from auto to the slowest setting

 

I don't want to interrupt but how do you manually set the latency?

 

Enter bios,keep tapping delete when the computer first boots,go into dram configuration 'it varies between motherboards and bios as to where its located',if you cant find it download your motherboard manual,if you cant find it in there your mobo may not have the option,then its a case of finding the each setting and lowering it,for example if your memory settings are currently 2-2-2-5 you may try to lower it 3-3-3-8,you may also want to try dropping the the command rate down from 1T to 2T,the idea is not to leave any memory settings on Auto as the different modules send conflicting ID's to the bios

Check this out for a brief explaination of what latencies are and what to look for in your bios

http://techreport.com/etc/2005q4/mem-latency/index.x?pg=1

 

Post your exact Brand & model memory.
These DFI boards are picky about hardware, such as memory, they do not like Value memory, it's not that cant run it but are more troublesome.
I suspect your running two different types of Mem Chips.
There is more to Memory than just DDR400/PC3200, example Lot's of the 2x1GB kits use Samsung UCCC chips, 512mb sticks can be TCCD, Bh5 etc. (FYI, there are other types of chips in both 512mb & 1GB modelus, TCCD is not avaible in 1GB sticks, to add a bit more info even the same brand can use different type chips in thier pc3200 memory lines)
Each of theses sticks while being pc3200 have different voltage requirements & timmings thus mixing different types of chips will lead to failure.

Can you or have you tried to run the 512mb memory chips by them selfs?
I'll assume your running mem by SPD, you can use Everest or CPU-z er even A64 Tweaker to find the speed/timmings your running at.
Most of the time you can look at the memory sticks if they dont have heat spreaders to see what type chip they are.
Are you OCing or running stock speeds?

 

Yes the 512 sticks by themselfs work fine, same with the 1gig sticks....but together they wont boot. I cant get into the bios with both in b/c as soon as i hit the power button the system starts beeping at me. Can i change the timings in the bios before i put them in, or do i have to have them in for the bios to pick up on the timings? But anyways maybe i will just get 2 more of the same 1gig sticks i just got, and hopefully that will work. Thanks for the info guys, appreciate it.