So I was installing MoBo drivers in Windows 7, fresh install. I left my phone plugged in to USB (for charging) during the installation of the USB controller (dumb move). During the installation process, the computer locked and had I had to do a hard reset. The computer wouldn't POST afterwards. I've tried 5+ times, unplugging PSU and discharging any capitance with the power switch on the case. No luck.
Thinking that the computer got into some wonky state, I removed half of the DIMMs (I have 4) just for s**ts. Then everything works fine and has been for the last few days and after numerous resets, even with the other half of the DIMMs re-installed.
Do you guys/girls think this a RAM issue? I thought *all* registers in the RAM are cleared on power-off. Period. Why would removing the DIMM make a difference? I tested the memory with memtest86+ and it all passed.
Sometimes when a device capable of delivering its own power is attached to a USB port the computer is still receiving a small amount of power which prevents it from resetting when you unplug the PSU. I have had this happen when I had a powered USB Hub attached to a PC. It is possible that your Cellphone battery was able to provide a charge to the USB subsystem on your PC. It is a theory on my part and may be incorrect. However as itzdanielp has stated your system is working fine and there is probably nothing to worry about.