This is the strangest technology problem I've had in a long time. I recently got a new TiVo HD and I've discovered that its remote control doesn't function, but only in the dark. During the day, or if there are lights on in the room, it works perfectly. But as soon as its dark, it goes blind. About 90% of the commands from the remote are never detected.
I've had a TiVo since 1999, so I have several remotes left over from previous models. I've tried them all, with the same batty and extremely frustrating results.
So I finally swallowed my geek pride and called TiVo customer service. It turns out that this particular TiVo model is sensitive to IR interference. If another device is transmitting IR, it can get confused. In my case, the culprit turned out to be the Wii sensor bar. Covering it with a thick cloth pretty much resolves the problem. (Although the TiVo still isn't as responsive as the Model 2 it replaced.)
The nice TiVo tech support person said that an XBox 360 and some models of TVs can broadcast interfering IR, too. I'm betting that X10-to-IR or any kind of IR repeater could also be a problem. So if you're suffering with a blind TiVo, start covering potential sources of interference and see if it helps.