Who knows why it works, but the method that has the highest chance of fixing even your most complicated computer problem is the simplest: just shut everything off, wait a few minutes, then restart. Internet connection go out? Restart. Browser acting up? Restart. Menu bar gone missing? Restart. Printer won't print? Restart. No sound coming from speakers? Restart.
If the simple restart doesn't fix the problem, the next step is to make sure that everything is completely shut down, perhaps even unplugged if you're the superstitious type. Wait for 30 minutes, then try again.
Then, and only then, if the problem is still there are you allowed to call your favorite geek for help.