My XPS 420 came with 2 x 1gb Hynix PC2-6400 CL6 chips.  I'm looking at upgrading it to 4gb and bought 2 x 1gb Corsair xms2 dhx PC2-6400 CL5 chips as recommended here http://accessories.us.dell.com/sna/category.aspx?c=us&l=en&s=gen&category_id=4325&mfgpid=194056&chassisid=-1

Because of the heatsink on them it was easier to swap the existing hynix ram into slots 2 and 4 and put the Corsair in 1 and 3 but the PC would not post - it just produced error beeps.  I took the Hynix out and it still just produced error beeps.

I swapped the Hynix back into 1 and 3 with the corsair in 2 and 4 and it booted windows and reported 3.25gb (some lost to 32bit os). I figured I would just plug it in and it would stay at 800mhz and run at a slower latency of CL6 to match the existing ram.  Instead the system lowered the ram speed to 667 which the Hynix is rated as cas 5 at and ran both sets at CL5.  Unfortunately, shortly afterwards, Windows blue screened and wouldn't load again with the Corsair ram in.  It's fine if I take it out and leave the Hynix in slot 1 and 3.

It looks like it'd be easier to get matching chips to the existing ram but I cannot get the exact model anywhere.  I can get ram that has the same timings though, something like Crucial PC2-6400 at CL6 - is it likely to work with the existing ram?  It's not the end of the world if I have to get 4 new matching ram chips but it doesn't help me if the PC won't post with new stuff in slots 1 and 3.

So does anyone have the corsair ram working in an XPS420? On it;s own or with the existing ram?  Or can anyone recommend ram that does work with the ram that ships with the system?  I'd rather have something that will keep the ram at the higher speed of 800mhz, and if the solution is to replace all the ram then it makes sense to get 800mhz ram that will go at CL5 for more performance.

 

Thanks