Some people resolved the issue by removing the CPU and straightening the bent pins in the socket.
During installation of CPU, some pins may have been bent. Since the memory controller is in the CPU, it may not have full control over memory due to bent pins.
Motherboard sees 8 GB RAM. CPU cannot control 8 GB RAM due to its crippled memory controller. BIOS confuses what to report about RAM, then decides to report 4 GB.
There is a CPU utility called CPU-Z, which can be found @ http://www.cpuid.com/softwares/cpu-z.html
, to get info about your system.
Be sure to download the correct version 32-bit or 64-bit for your Windows.