Here's a relatively simple fix you can do if your Dell laptop is getting overheat issues.  Of course, legally, I am going to cover myself by saying that if you attempt any repair on your own computer, you accept all responsibility for doing so.  As with any finely tuned electronic instrument, your laptop is fragile, and there are many ways a repair can go wrong, including static discharge, breakage of electrical connections, scratching of finished surfaces, and the like.  None of my posts or comments should be viewed as anything other than for information purposes only.  You should seek professional help with getting repairs done on your own system.

Now that we got that out of the way, let's take a quick look at this.  The customer complained her laptop was getting extremely hot during use.  So hot, in fact, that it would burn her leg or arm if she came in contact with the bottom of it.   Additionally, after a prolonged period of time, she said the laptop would shut down during use, after getting very slow.

The buildup of excess heat is very dangerous for your computer- especially your processor and graphics components.  High performance components work much better when cool, so one of the first signs of overheating processor is slower performance.  The processor is moving electrons at a high rate of speed.  Higher temperatures mean agitated atoms that are less orderly.  Just like taking a classroom filled with kindergarteners through a doorway, the endeavor works much faster if the children are calm, orderly and walk in a single file line.  The flow of children slows dramatically, if they are bouncing around, talking, and agitated- or if they all bolt for the same door simultaneously.  So a cool processor can pass electrons through its channels at a much higher rate of speed if those electrons are in a calm, low energy, low temperature state.  Science geeks, there's your fix.  Please send your technical hate mail to my inbox.  I'll be sure to read it.  /sarcasm/

The customers complaints were obviously relating to some kind of interference with the cooling process.  On Dell laptops,  as with moth laptops, the cooling system consists of a small electric fan that blows air over a heat sink.  The heat sink is literally touching the processor.  As the processor works, it produces heat, and that heat conducts itself into the heat sink- which means the heat sink gets very hot.  The fan blowing air over the heat sink indirectly (and more efficiently) cools the processor.  BUT... and this is a big but... if the heat sink has been encrusted with dust particles, the dust coats the heat sink and acts like a fluffy thermal blanket.  And we all know what happens under a thermal blanket.  Heat gets trapped and cannot escape.  The processor continues to work as its temperatures climb.  Electrons at a higher energy state become disorderly and agitated and bounce around.  They don't flow as well, and the user experiences this as a slower computer.  Eventually, built in motherboard features simply shut down the computer altogether and the user may experience a series of errors, followed by sudden shutdown.

Besides slow performance and sudden shutdowns, the excess heat can completely destroy the processor or the motherboard.  How so?  The repetitive heating and cooling, heating and cooling makes the material in the motherboard expand and contract, expand and contract, day after day.  If you can imagine bending a paperclip back and forth repeatedly, eventually it becomes brittle and after a dozen times, it can break completely.  The expanding and contracting on a motherboard will not break in half, but just like a hot sidewalk, it can develop fine cracks.  If a crack develops in an unfortunate location, it may prevent circuits from closing as they were designed.  The end result:  a "fried" motherboard with a hairline crack on any one of its thousands of circuit tracks. Because they are so tiny and fine, there's no efficient way to find where these cracks are located, and therefore no cost efficient way to repair them.  A "fried" motherboard is good for the recycling company, and pretty expensive to replace.