8 GB RAM installed (3.98) usable

This problem seems to have run for some time.
To try to solve issue may I note I have 2 systems with this specific MOBO and 8Gigs of ram in each. They show 3MB held for hardware. This machine should be running Windows 7 64bit for best performance and memory utilization. 32bit OS's only support 4Gigs. After a year of continuous running these machines are just fine compared to the issue the OP has raised.
Reseat the RAM and see what happens. Also be absolutely certain the OS is indeed 64bit. You can install that version in place of the 32bit using Gregrocker's Tutorials. The benefit is that you only pay for the OS 1 time regardless of version. That's my 2 cents.