Precision M6500 - screen shut off

I'm wondering if it overheated. I have an i7 version of the M6500
running Windows 7 64 bit. I came back from lunch and the machine was
asleep. I hit the power button (it was flashing slowly) and the screen
came on and I got back to work. After about a minute the screen went
completely black. Fans were still running, hard drive light was
flickering randomly, and the machine was acting normally. Just not the
screen. The backlight was completely off, and I couldn't see the faint
impression of the pixels changing colors. I've seen that before. I held
down the power button and it restarted normally and I haven't had the
problem since. Normally I put two erasers under the two rear feet to
keep the machine about a quarter inch off the table's surface. That time
I didn't.