RE. stettybets comment about high density. It's certainly possible that this is the problem which is why I enquired about the second module as well. Although from the link you gave me, it would appear that that particular module is dual-banked...
Given that the you have bought the correct type of memory (i.e DDR2 667), then a likely explanation is that your system is not compatible with high density (a lot of systems aren't, especially branded ones like Toshiba).
Your best bet is probably to return the 2 modules & get a refund. When it comes to buying some different memory, I advise you go to somewhere like Crucial or Kingston and purchase it directly from them. The reasons I recommend you do that are:
1) It's rarely worth buying generic memory (such as the one in the link you gave me). Generic modules are often inferior, hardly any cheaper and come with limited warranty. Decent stuff (such as Crucial/Corsiar/Kingston/OCZ etc) come with a lifetime guarantee
2) Both Crucial & Kingston have an online memory advisor. This means that if you use the memory advisor tp select your ram & buy it from them, they will guarantee that its 100% compatible.
If for any reason, you end up having to buy the memory elsewhere (for example, if one of the stores won't give you a cash refund on your current memory & only issue a credit note), then be very careful what you buy. Your system should be compatible with either DDR2-667 or DDR2-533. For 2GB modules you need a chip configuration of 256Meg x 64 and make sure it is low density (not all resellers tell you this though).
Also bear in mind that your laptop supports dual channel memory. To take advantage of this, you must ensure that both modules are absolutely identical, not just in speeds but also in timings etc so if you want to buy 2 x 2GB, then a 4GB kit would be the best way to ensure they match exactly.
Edited by Samm, 22 February 2008 - 08:10 PM.