System Restore is a great tool, when you need it. The point I intended to make is that each use of System restore is likely to reduce the stored group of prior sytem records that you have available, and gratuitous use, before thinking a bit about what the real problem is, can actually make system restore unable to help you.
A reboot actually accomplishes a fairly comprehensive system verification, and can restore many corrupted files. The .dll files that contain a lot of the scripts that tell devices on the machine about settings and options get rewritten while the computer is running, and are subject to some occasional corruption. Often the reboot alone will bring them back. (Game programs that set new monitor settings or define special uses for keys on the keyboard are a common "corruptor," if they don't return the non-game settings correctly when you quit playing.)
Once obvious hardware glitches are eliminated, or when you've made a recent system change that might have introduced a new problem, System Restore provides a good way to get everything back.
And if you've got enough cat hair around to foul the keyboard, as I do, don't forget occasionally to vacuum out the airholes on the computer. When the furballs block the fans, components can start to make smoke (usually invisibly) and all kinds of exotic things can happen - sometimes expensive things.