It is my understanding that the game is even installed under the user directory instead of "Program Files" so it will not need elevated permissions when patching. I am running the game under Windows 7 Ultimate 64 bit and have encountered no problems with the game or my system that weren't due to ATI video card drivers.
I can think of only two probably causes to your experience.
1.) Hardware failure. PC components DO fail, often times in unexpected ways. For example I had just told a friend I needed to reboot my system to swap from Ubuntu to XP. As soon as I was about to select which OS to boot into the main memory module, a 1gb module decided to short out. Result was 20 minutes of troubleshooting and falling back on a 128mb stick from an earlier upgrade. Also had a power supply work fine one day, then the next morning make angry buzzing sounds blowing a UPS, surge strip, and circuit breaker...
You could try checking the cables to see if they're properly connected, a loose power or data cable could cause the drive to not be detected or spin up.
2.) If its a networked drive then the host system for the network drive is not responding, either due to a faulty network cable, LAN card, failed login, or bad drive mapping. Or the drive/data might not be shared any longer.