Will flashing BIOS fix "unseen" second DIMM?

Probably not. Are you sure you do not have a bad RAM slot?

The RAM slots are OK -- there is a 1GB and a 512MB DIMM in them now. When the new 1GB DIMM is installed, the BIOS won't see either one of the 2 existing DIMMs, no matter which one is installed.

That's pretty weird. I guess you can try flashing your BIOS but I don't think it will help.

Maybe you got a bad stick of RAM?

Hi,

Flashing your BIOS unfortunately will not fix the problem.
You were using two different speeds of memory and with different specifications/voltages. Try getting the exact duplicate of the first 1GB stick. If that doesn't work, and if you know how to get into your BIOS and it has a memory tester, use it. You might have fried the memory controller...

Does your machine boot at all? Can you access the BIOS?

Cheers,

Greg

Thanks to all for your responses. I got another 1GB stick and that worked with the other new stick. My guess is that the original 1GB stick runs happily clocked down to match the PC-4200 stick, but does not work at full speed when matched with another PC-5300 stick.