Turn it off. All the way off. With no power. For about a minute or so. Then power it back on.
This works wonders on many problems with many different types of equipment, including desktops, laptops, phones, monitors, small appliances and most anything more complicated than a toaster. Heck, it might even help some toasters.
The reason this works is that most electronics have self-resetting circuit breakers and/or an embedded processor (be it a CPU or audio DSP, etc), and powering these off all the way allows the circuit breakers to self-reset and any processors to do a cold reset whereas they may otherwise be getting a little power and staying in some form of error state.
I've used this many times in the past, but three times very recently it has worked magic for my family who were already planning to pay to fix or buy a replacement device.
My sister started tweeting recently from work that her Droid was dead. It wouldn't power on, and it's her hub of communication. She had tried different chargers, powering on with the charger connected, everything she could think of. She was planning to stop by the Verizon store later in the day and bracing for an expensive repair or replacement. I asked her if she had taken the battery out for 30 seconds or so then put it back in. She messaged me back a bit later with much praise for my genius as her Droid was working fine again. (I hope and presume that the Verizon store would have tried this and "fixed" it for free, but I at least saved her the trip.)
Just last week my mother was asking if I had a spare wireless USB adapter or if I could fix hers for her TiVo as it has quit working, and the light won't even come on even if she took it out and reconnected it. I said there wasn't much practical to do to fix them, then I suggested she unplug the adapter, shut the TiVo all the way down, unplug it for a few minutes, then bring it all back up. She called me back later that day also telling me of my genius because it was working fine again. Note that in this case the host device getting powered down is what fixed it. If your malfunctioning widget plugs into something else, then perform the magic fix on the widget and the host at the same time.
Last night I was trying to watch some YouTube videos on my netbook, and my netbook would get some static-y sounding noises, stutter and then lock up completely with a very unpleasant un-netbook-like buzzing noise. I hard-powered it down each time, rebooted and tried again, but it froze on several different YouTube videos. I was already planning how to work around this apparent audio processor hard fault while still enjoying my netbook when it occurred to me to try the magic fix. I had already powered it down several times, but I hadn't removed the battery. So I powered down, removed the battery for about a minute and started back up. Now I can watch all the YouTube I want again with perfect audio and no stuttering or lockups!
Remember it doesn't have to be a smart device for this to work. Way back in the day I fixed several dumb non-multisync CRT SVGA monitors by unplugging them for a few minutes. In these cases there must have been a self-resetting circuit breaker inside, but you have to take it off power before they reset.