Why is my system doing this? See details.

Using Vista Ultimate 64 bit. I just bought a battery backup a few days ago into which I put the computer and the monitor. When the computer is idle, it goes into some sort of sleep. The screen is black. Moving the mouse gets no response. Hitting keys gets no response. I have to press the power button on the tower then the monitor will show that the system is assigned to me, locked (which is fine). This only started since I bought the battery.

Any ideas?