Just in case it interests or might help someone -
Anyone reading Win_7 related forums will have seen stories about (even if they haven't experienced) problems with Windows only being able to use half the installed RAM, crashes, lock-ups and BSODs.
My current machine -
16 Gb Kingston RAM
1 Tb Seagate SATA drive
nVidia 8800GTS + nVidia 430 GT
3 x 19" monitors @ 1600x1200
- started off fine (apart from seeing only half the RAM) but gradually developed all the other problems at ever-increasing frequency.
I tried all the proposed cures - reseating the CPU, switching RAM modules around, updating drivers - including the Intel chipset drivers that Windows Update does not update, reformatting the HD and, finally, dropping back to WinXP-x64. All to no avail.
Now I have rebuilt the machine on a new mobo - ASUS P7P55D-E and, hey, no problems and all 16 Gb of RAM is useable.
I doubt that ASRock mobos are all bad and ASUS boards are all good but I suspect bad quality control in one or more of the common component parts - to me, the P55 chipset seems the likely culprit.
Of course, bad things might still develop ...