Compatible Memory Upgrade for Toshiba Satellite Pro

My old laptop is a Toshiba Satellite Pro L300 1Af with a maximum upgrade capability of 4 GB. Crucial's System Advisor couldn't recommend any compatible memory. There are two of these modules fitted at the moment: I replaced them with two of the modules above. It's over a month since I ordered them, so I can't remember why I chose this type, maybe I looked at a YouTube video on upgrading this model of PC. Anyway they don't work, and the system doesn't attempt to boot. I presume the bus speed isn't compatible with them (Crucial says its 667 Mhz) or they're faulty. Both the new and old are PC2-64

Question by Eugene Brennan on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.