Are you talking about your remote control or your wireless gamepad?
If it's your gamepad, just hold down the guide button on the gamepad for a couple of seconds to turn it on. As long as you have already synced it once, your 360 will find it and assign it a port number.
If it's the remote control, you could try checking your system settings to make sure it's set to accept all remote controls rather than just the media remote.
Thanks, yes gamepad is what I was looking for - I will try that after I Google "guide button".
The Guide Button is the one in the middle of the gamepad with the big X on it.
Do the game pads go to sleep after a specified period of time?
Yes, they do. The gamepad will shut itself off to conserve power after you stop using it for a while. I'm not sure exactly how long, but it seems to be around 10 minutes.
If it does it while you're in the middle of a game the Xbox will behave as if the gamepad was wired and unplugged. In other words, it will pause the game and ask you to reconnect and press Start before continuing. (As I said, just hold the Guide Button for a couple seconds to reconnect.) So no worries.
To shutdown the console or the gamepad, hold the Guide Button for 3-5 seconds and the Shut Down menu will pop-up. It's handy for shutting down the console if you don't want to get up, but it's not the fastest way to shut off the gamepad. For that just disconnect and reconnect the battery pack. :wink: