Can't get pc to recognise 2gb memory

I've got an HP M7520 multimedia pc which has 1Gb of ram fitted. Trying to upgrade it to 2Gb and having no success. Pc currently has 4 x DDR2 4200 256Mb dimms and works fine. I've tried adding 4 x 512Mb 4200 dimms or 2 x 1Gb 4200 dimms (all of which work in my Dell 5150 with no problem) but both sets of dimms result in the same problem. The BIOS sees the correct amount of memory. Booting in safe mode works with no issues and XP sees 2Gb of memory. Booting normally results in the machine just hanging on the windows XP splash screen with the bar at the bottom just continually scrolling. Anyone any ideas?

First thought would be that the memory is incompatable with the mobo - only reason I can think of it working in safe but not normal mode is that some particularly demanding driver is being loaded.

First off I'd try running memtest 86+ to give the memory a good testing, and if it passes that, then do an interactive boot of XP to see (if you can) what is causing the system to hang. The bootlog might be useful.

What do you mean an interactive boot?

latest is: any 2 sticks of the 512 dimms work, either of the 1gb sticks on it's on works. So it looks like XP just doesn't like 2Gb of memory on this machine.

thanks!

right, this is weird. I can put up to 1.75Gb into the machine and it boots - either 3 x 512 and a 256 or 1 x 1g a + 512 + 1 x 256. Definately looks like something weird when only 2Gb is present. Anyone?

this is even more weird - if I fit more than 2Gb it boots! wtf????

Don't suppose there's a bios update available?

Have you tried getting 2GB by using 1Gb + 512 + 512?

If that works then I'd suspect there's an error with the Dual Channel mode of your motherboard in conjunction with the type of RAM you're using (is it High Density or Low Density?)

Tried loads of combinations and any combination in any order that gives 2Gb will only boot in safe mode and doesn't boot in full mode (1+1, 1 +512+256+256, 1+512+512). Any combination that's not 2Gb boots. Boots with 2.25, 2.5 and 3Gb. Never seen such a weird fault. Just going to leave the system with 2.5Gb in it (2 x 1Gb and 2 x 256Mb) and forget about it ........

System has the latest BIOS.