The setup...
GA-H61M-USB3-B3 rev 1.0 with latest F5 BIOS. Optimized Defaults loaded after BIOS upgrade.
BIOS Health page shows all voltages, temperatures, and fan speeds to be fine.
WD WD10EARS 1TB SATA HD (green) in SATA2_0 port, Samsung DVDRW in SATA2_2 port. Boot priority is CDROM/Hard Disk/Disabled.
Single 2GB DDR3 SIMM in DDR3_1 slot. Passed 3 passes of Memtest86++ v4.20 without errors.
Intel i3-2100 CPU.
Fresh install of Windows 7 Home Premium SP1 x64 on the above HD, with BIOS SATA AHCI Mode set to "AHCI" *before* the install.
All MB chipset, LAN, video, USB3 drivers installed. Didn't install the Realtek audio drivers, sound works OK with the MS audio drivers. No devices in Device Manager with (!).
The problem...
Sometimes (~50/50) when restarting from within Windows, the PC will restart again just after getting to the "Starting Windows" message, or at the same point it will power off (fans stop) and then power on again.
If it does either of the above, sometimes Windows presents the "Windows Error Recovery" screen with "Launch Startup Repair (Recommended)" or "Start Windows Normally" options, or sometimes it will boot normally to the Windows 7 logon screen. If I select "Start Windows Normally", it launches Windows fine.
It seems to take longer than necessary to start booting from the HD. Looks like some details about the drives appears (AHCI related?), screen clears, then the "Loading Operating System..." line appears, and then underneath that more '.' appear roughly 1 per second, with no hard drive (or DVD) access until the cursor is below (IIRC) the "s" of "System", roughly 20 seconds.
Gut feel is that it's somehow AHCI mode related. Can't prove it, just a feeling. I know there can be problems turning on AHCI *after* an OS install, but is it possible to revert to IDE mode without any issues?
Ironically this build is to replace a friend's problematic old PC.