i have the same problem with my Toshiba Satellite L500, it has Windows 10 with 12 GB of ram installed but can only use 2.99GB. its made my computer slow when i play small games..
1| Can you please state the SKU for your Toshiba Satellite? There are too many to keep track of.
2| Have you made sure your BIOS is up to date?
3| Can you please state which rams you used to achieve 12GB's of cumulative capacity? I'm assuming you used a 4GB + 8Gb stick of ram.