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!