hi, I had 512mb ram (super old, I think it was PC400) in my computer, Best Buy had a sale on Kingston 512 3200, so I bought some. My motherboard (also 5 years old) can support 1G ram but only up to PC2100. I've read everywhere that memory is backwards compatible as long as it's the same type (DDR, DDR2, etc). I buy it and put it in (had to upgrade the bios for it to work) and it works fine. Except randomly, usually while I'm in firefox, firefox will crash then keep crashing immediately on reopening the program. Then I get a blue screen about a PEN_LIST_CORRUPT. I've read that means bad ram, but I ran memtest 86 with 1 stick at a time (once in each slot) so a total of 4 times and no errors. Then I try it with both sticks in, and sometimes I get errors, and other times I stop it at 300% with no errors. what's going on? The individual ram sticks don't seem to be bad and the slots are fine. Windows reads it at .99 Gb (when I upgraded the bios it seemed to take a larger chunk of it away, but the bios upgrade was required for 1G ram). So, any suggestions? it's been under 30 days since I got it, so Best Buy will probably take it back if it's bad, but it seems strange. I'm gonna run memtest again while I'm in classes today and see what happens this time. Thanks!

Incompatible memory modules/sticks. Send it back and try another one. Memory sticks with the same speeds may not always be compatible to each other.

I am currently running 2 brand new sticks of 512 MB Kingston PC 3200 DDR ram, I can't imagine how they wouldn't be compatible, they're exactly the same thing. I still have my old ram, but it is not in use, I only have 2 slots. So, if you meant if I had any of my older ram left, I don't, sorry for the confusion. Thanks for the reply.

I thought they were an old and new sticks installed together in your system. If you are sure that your old stick is ddr400, you can also use it along with a new stick (ddr400 and pc3200 are both the same). Try it.

If your operating system is 98/ME, you may not run it successfully with 1gb of ram.

When I had mixed ram, before my bios upgrade it did the exact same thing. I had to upgrade the bios so that it wouldn't fail on boot with a PEN_LIST_CORRUPT. I run a Gateway 500 SE with Windows xp and the original bios only supported 512MB, but the motherboard supports up to 1G, so I updated the bios, which fixed the problem (mostly), and then I could boot and operate the system normally.

I left my desktop at school since I only came home for labor day, so I can't switch them until monday, and then my 30 days for my ram return will be up, so if possible, I'd like to keep using my new stuff, but it's worth a try. Is there any further suggestions? I'm also gonna reinstall/upgrade firefox since it seems like that always starts it. That may just be that that's the program that is open the longest, so there's a higher probability that the problem would happen when it's open. ok, thanks for the reply!

Try to mix the ram again or reinstall the new ram sticks and reinstall firefox or install another web browsers.

a 3rd option has opened up as well. As seen in my other threads, Im scavenging on my mom's old computer, her ram is compatible with mine, so I'll try maybe 1G of slightly older ram and maybe just return the new stuff and save $60. But I'll have to see when I get back to my dorm. Thanks for the replys.