I think we have talked about this before. It is just a kernel-limitation in non-server editions. 3rd party software is welcome to use the memory that Windows will not.
How to enable more than 4GB of RAM in WIN 7 32 bit, only 2.87 usable.
Most of these replies are bogus. Go to Microsoft.com and search for this as they provide the answer. Just as a note, using 3rd party apps to hack the KERNL may leave your system totally open to attacks.