Computer memory/motherboard problem. Any ideas?

[degeneration]

Can anyone explain why the following happens with my comp?

I recently bought 2 x 1GB DDR2 memory sticks for my comp to replace its small 1 x 512MB memory. The memory is compatible etc.

My motherboard is a Asus P5VDC-X and it has 2 slots for DDR2 memory.

Now when I put either of the memory sticks in on its on, in either of the 2 slots, it all works fine. So clearly both sticks work, and both slots work.

However, when I have both the sticks in at the same time, the system is quite unstable. It has spontaneously reset itself quite a few times , not started up properly on several occasions and just generally doesn't seem like all is going good.

Why could this be? I'm not techie enough to know anything about this sort of thing, so any help will be apprecaited.

Cheers.

[IronMonkey]

What frequency is the RAM supposed to operate at?

[bradavon]

You didn't say what speed RAM you've got. I take it you know your motherboard is compatible with the speed you went for? (e.g - PC3200).

[degeneration]

Ah sorry, missed that out.

I THINK I've sorted it, but will wait and see over time.

It was 666Hz memory, which in the motherboard bios that was stated as being supported, although the manual only stated up to 533Hz - possibly due to 666Hz memory not being around when the mohterboard was made?

Anyway the memory it replaced was 400Hz (or something like that) 512MB stick.

I've got a feeling that as the memory was being run at 666Hz, it required a greater voltage, which the mobo wasn't supplying, so the computer cut out.

I've manually reduced the frequency in the bios to 533Hz (as that is the highest quoted value in the manual), so hopefully that will mean it only requires the voltage that hte mobo supplies to the ram, which I'm hoping will mean no more cutting out and restarting.

There is no option to alter the specific voltage for the ram in the bios.

Anyway, like I said, if it works fine and doesn't cut out, problem is solved. If it does happen again, then I'll be annoyed, and will have to start thinking about it agian.

[IronMonkey]

I think you'll have hit the nail on the head, hopefully your problems are solved.

[bradavon]

Why would the manual and motherboard state different supported values?

[degeneration]

Possibly manual was written with one theoretical max frequency, then at a later date in an updated bios it allowed support for the 666Hz... although given the problems I had, and the fact that it hasn't crashed since I changed the frequency down to 533Hz, it clearly itsn't properly supported yet.

[EvaUnit02]

Have you set the correct voltage in the BIOS setup? When I installed my old DDR2-1000 modules my computer would keep crashing because the modules weren't drawing enough power. V2.1 is was the required voltage, I was running them at V1.8.

The voltage requirements should be listed on the RAM's packaging.

[degeneration]

Unfortunately as I said earlier, there isn't any option to change the voltage in the bios setup. Only can change the frequency and a few other things that are detailed above.