I have a Lenovo W500 type: 4061-2ZG running a 64 bit Windows 7OS on it. I have 2X4G ram memory from Kingston “KTL-TP1066/4G”. The problem is my machine recognizes only 4G instead of 8G that I have installed.
Generally a good quick test approach when 2 modules are involved and the amount of memory short is the value of one of the modules, is to remove one module and see if the system recognizes the remaining one. If so, swap it and repeat. If it doesn't recognize it, then the second module is defective. If it does, then potentially the board has a bad slot.
Software diagnostics can be helpful as well.
Lenovo's diagnostic - Lenovo ThinkVantage Toolbox contains memory tests and may be helpful for use on ThinkPads, ThinkCentres, ThinkStations, ThinkSevers, and some older 3000 model family systems.
You may also elect to try 3rd party software such as memtest+ and / or HWmonitor and see if it reports two ram slots or one.
If this is a new installation of upgraded memory, and this configuration has not been previously proven on your system, update to the latest level of BIOS.
Additionally, ensure that the proper speed and type memory is being used. Some 3rd party memory types may not be compatible, or may not be compatible in combination with other manufacturers. Use matched pairs for best performance when possible.