I'm currently trying to upgrade my old Sony VAIO VGN-SZ1HP/B to 2GB of RAM. It already had 1GB of Crucial RAM in one of its slots, and one empty. I checked on Crucial.com and it confirms that each bank can hold 1GB of PC2-5300.
The 1GB stick already installed was this, but Crucial's page recommended this... The two are identical from what I can make out, so I just ordered another one of the former. Unfortunately the machine refuses to even POST with both sticks installed.

If I remove the old RAM from Slot 1 and replace it with the new RAM it runs fine. If I leave Slot 1 empty and put RAM (either stick) in Slot 2, it won't POST.
Basically it seems that Slot 2 just isn't working properly.
Does anyone have any ideas on how to solve this problem? Or perhaps has some experience with this sort of thing with Sony VAIOs?