if your system allows 4gb and the system only reads 3.1 GB theres somthing wrong is the memory being read minus the video being shared or, yet is your system video use shared memory and if it is how much, does it account after the video shared is minus from the main memory

try isolating the problem since this whole thing started only after you upgrade, try the old memory back and see what happens or better yet, try the memory one by one,analyze then isolate, this are the best steps in troubleshooting.

Just for the record, a 32-bit Windows operating system will recognize up to 4GB of RAM, but will not show the total amount because of the draw from critical functions such as the system BIOS, motherboard resources, memory mapped I/O, AGP, PCI, PCI-E, and other memory allocations for PCI devices.

Different onboard devices and different add-on cards (devices) will result in different total memory size. This means that the more PCI cards installed will require more memory resources, resulting of less memory free for other uses.