I recently added a 2GB memory stick to a TravelMate 5740 laptop running Windows 7 32-bit which already had 2GB of RAM. I am aware of 32-bit systems not making use of the full 4GB memory, but I was expecting actual usage between 3GB and 3.5GB. Instead, Windows reports 4GB installed, 2.3GB usable. This is not your average "where is my memory" question, and I don't think it is a duplicate. 2.3GB of usable memory out of 4GB installed is unexpectedly low even for 32-bit systems. Graphics card is an Intel shared-memory one that uses 128MB. Can anyone explain this? Can this problem be "addressed", pun intended?
Here is something you are forgetting to mention:
If you have a graphics card that is not a dedicated Graphics card then it probably uses up memory from your computer.
For instance, I have an HP Pavilion G6 and it has a Radeon HD 6470M graphics card. It is a 1.5 GB graphics card and it is not dedicated.
Because of this, I am only able to use 4.5GB of the 6GB of RAM that I have installed. The graphics card uses the other 1.5BGs. A dedicated graphics card has its own RAM. If you have a dedicated graphics card and you have 6GB of RAM, then you will be able to use all 6BGs.
Unfortunately, on 32bit systems hardware address spaces get mapped into the 4GB address space of your memory hence the reason why you never can really fully use the 4GB installed. Usually, one of the biggest culprits is the graphic's card's memory. Since yours only uses 128MB your available size is quite baffling, but who knows what else is mapped into the address space by your BIOS and to what extent. There are several things you can try though:
Open a command prompt and enter "BCDedit /set PAE forceenable". Then reboot, enter your BIOS and check if it has an option that allows for memory remapping. If so, activate it. Boot into Windows and check your available RAM.
If this doesn't help then the only option would be to upgrade to a 64bit version, or use software that makes use of the unaccessible RAM through other means such as a RAM-Disk.
Edit: I just checked. Your laptop is equipped with a modern Intel I5 which should support 64bit operating systems, so there's really no reason not to upgrade.