I am trying to upgrade the memory to 2GB. The computer will not boot with both new modules inserted (2 Crucial 1GB modules PC2-4200). It will boot with 1GB installed in either slot as long as the original 256MB module is inserted in the opposite slot, but will not work when both 1GB modules are inserted. There are 2 slots and the maximum is 2GB for this computer. I was told to update the BIOS which did not work. I am currently using 1 of the 1GB modules and the 256MB module that came with the computer.
I have a Toshiba Satellite A105.

Apparently there is some kind of conflict between your Crucial memory modules and chipset on the motherboard. I guess you’ll have to use different memory brand, try Kingston instead.
I just checked witch 1GB memory modules Toshiba lists for Satellite A105 laptops. The mention the following brands: Samsung, Hynix, Elpida.