Start by removing power to it for at least one minute. Then back on. If that doesn't reset it, you'll probably have to replace it.
(They've gotten really cheap in the last couple of years.)

I believe that there is 2 adjustment knobs on the sensor itself. One will adjust the sensativity of the motion it detects and the other is for the time the light stays on. Play with it and you will probably solve your problem.

www.joetedesco.com

[This message has been edited by Joe Tedesco (edited April 09, 2003).]

With mine, you can make it stay on all the time by shutting off power momentarily, then back on. (Fortunately, it has a switch.)
To make it go back to "sensing" mode, you power it off for 30 seconds or so, then back on. You might have to shut off the breaker for that circuit if you don't have a switch.
You probably had a momentary power outage that set it "on", and now you can't get it to go off.

[This message has been edited by rpxlpx (edited October 11, 2002).]

I have one on my barn that does the same thing when its wet out. Of course one of the attaching screws is missing, so I assume thats why, I'll have to get a round to it one of these days.