FP monitor won't work with batteries!

[emschwar]

We've had the FP sound and lights monitor since our 3.5 year old was born. Now, we're using it with our 2nd child. Except yesterday, we took it off the plug and brought it upstairs like we usually do, and it wasn't working. No problem, we changed the batteries and it worked fine. Put it back on the plug last night when we were downstairs. This morning, I took it back off the plug, and it won't work! Obviously, it doesn't need new batteries.

Has this ever happened to anyone? Is there anyway to fix it? Or am I SOL and I have to buy a new monitor?

Thanks.

[Momof3Labs]

This happened to us with a different monitor, and we replaced the AC adaptor (available at Radio Shack) and it worked again.