Windows can cause problems. A storm sash can crack from old age, ice can cause a stress fracture, or water damage can attack the frame. But ignoring the problem, whether it is as obvious as a baseball through a window or something less subtle, is never a good solution. Even small problems cause energy loss, insect infestation, and moisture problems that can attack other parts of your house and your wallet.
Basic Window Maintenance
The most common cause of window damage is a lack of basic maintenance practice. Your grandma was right when she told you that you should wash those windows every spring and fall. In fact, in most locales you should do it far more often than that. Beyond clean windows, the added benefit of washing your windows is that you can see problems before they happen. You will notice if the wood is discolored yellow, or is soft (rotten), or if the sash is loose, and then you can immediately move to correct the problem.
Similarly, inspect the glazing putty for cracks or missing pieces, check all joints and seams, and even run your hand in front of every inch of each window on a cold winter day if you think there might be a problem. These small steps can prevent larger, more expensive problems.
The Quick Fix for Window Repair
This is always tricky territory. If you see a crack forming in the glass and want to keep it from continuing and shattering the glass entirely, a strip of duct tape can prevent further damage. If a crack is forming in the sash or frame, a bit of caulk can help. And if you find there's a draft, there are insulation kits that help you put a plastic seal (heat seal) over the window in winter. But the reason that this is tricky territory is that you do not ever want to rely on these fixes for more than the few hours or days it takes to get a window repairman over. These "fixes" do not seal the problem; only cover it up for a bit.
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When Do You Contact a Window Repair Professional?
Consider what happens when you poke a needle into a water balloon. More times than not, the hole grows as one force meets another. The water wants to get out. It is the same with a home. A small hole, a small problem, will always grow, and it will do it before you know it. The rule of thumb with something as important to energy consumption, safety, and the design of your home, is to always call when in doubt. Small problems grow quickly.
Windows deteriorate over time. That is a simple fact of home maintenance. The constant opening and closing, along with seasonal temperature changes, naturally cause issues over time. Consider it the price you pay for a bit of light in your life. Just don't neglect this important part of basic home maintenance, and call a window repair professional when you see a problem forming. 
Brice Particelli, formerly a carpenter in Colorado and Kentucky, manages continuing education programs for Columbia University and is a freelance writer for both the home improvement and travel industries.