I've had two hardware problems a few times over the last 2 months. First my NIC wasn't showing up in Windows XP even though it was registering ok in BIOS. I tried restarting and shutting down and a whole slew of other things but nothing worked. I saw someone with a similar problem mention that when they brought the computer to another house it worked. So I tried unplugging the power chord and switching off the PSU and when I reconnected them everything was fine.
A few weeks later I had a problem with my secondary drive not showing up in Windows (even disk manager), despite showing ok in BIOS. I restarted and shut down the computer for a few hours and it did nothing. On a hunch, I disconnected the power chord and turned off the PSU. Now it works fine.
My question is, what could be causing this? And why would disconnecting the chords fix the problem when shutting down wouldn't?