My laptop's stock RAM is a stick of Kingston 4GB DDR3 (1.35). I recently bought another stick of 4GB RAM but it is 1.5v and my laptop doesn't detect it but CPU-Z does. Can I actually make use of this RAM?
If you don't see it in the BIOS then Windows won't work with it. Did you try a BIOS update? Best idea is to return the stick and get one that exactly matches the specs of the existing RAM you have. You did not list the model of the laptop, some are limited to 4gb max RAM, and if you have 32 bit Windows you won't be able to use more than 4GB either.