I have a new custom-built Windows 7, 64-bit desktop using Intel Desktop board DH55PJ, Intel i5-760 Quad Core 2.80 Ghz processor and 8 Gb Kingston (2-4 Gb modules) DDR3 SDRAM.
One of the RAM modules has failed:
Windows reported the failure by listing only 4 Gb RAM in "Control Panel >> System"
Topala Software's "System Information for Windows" build 0714g reports only 4030 Mb of system memory in its "System Summary"
Speccy v1.09.231 reports 1 ram slot as unused but also reports available memory at 8060 Mb