It's a cliché at this point, but giving your computer a reset really can help. If the CPU is under a lot of stress, or some other unknown hiccup occurs, it can prevent the drive from showing up.

I have this XP SP2 Pro machine which always exhibit this behavior. Whenever I connect any external USB drive or flash drives, the computer freezes for a few minutes and after a while it says that the ...

If the drive is connected via internal SATA, then it's more the drive speed than the computer, so you'd be back to two-ish hours, depending on the drive. I'm assuming a write speed of about 150 ...