My laptop has 4 GB of RAM, but it only uses 2.6 GB of RAM. As such, my laptop can't run New Vegas because of the fact that all of my RAM are being used by my laptop's system. So, how do i make my laptop use all of it's 4 GB of RAM instead of just 2.6 GB ?

My laptop has 4GB also and it runs NV just fine. Try disabling any services or process you don't need (check http://www.blackviper.com/ site if you need help on that). There are also some mods you can use to improve your performance. I'll link some in a sec.

1. http://www.nexusmods.com/newvegas/mods/35262/? - Lets you use 4GB RAM but if you only have 4 it can't use all of it... Try setting your game to high priority as well.

2. http://www.nexusmods.com/newvegas/mods/51670/? - Lowers the memory usage of the game.

3. http://www.nexusmods.com/newvegas/mods/45116/? or http://www.nexusmods.com/newvegas/mods/45475/? - Both of these disable random clutter in the world that is hardly noticeable but can impact performance. Use only one.

4. http://www.nexusmods.com/newvegas/mods/46302/? - INI files with optimized settings for specific VRAM sizes.

5. http://www.nexusmods.com/newvegas/mods/40442/? - This program shows different settings you can edit in your INI with a GUI. Try the above first and then edit settings with this if you can.

In all the above, read the full description and read mes before you try them out.

Run 64-bit Windows instead of 32-bit Windows.