How many pairs of hinges does your laptop need? You know what a hinge on the laptop is? Yup, that thing which holds the LCD screen from the base of your laptop computers. Usually you just need one pair for each computer. Then why is someone trying to sell 5 pairs on eBay?
Probably because it is so easily broken, that people actually want to buy a few spares just in case.
You see, my everyday computer is a Dell Latitude D600, which I got from work 2 and half years ago. I do almost everything on it, and I reckon it is always doing something 12-15 hours a day, 6-7 days a week. It has quite a significant wear and tear with scratches everywhere. Worst of all, it has broken hinges.
A few months ago hinge on the right broke. It snapped and broke into half. Now I know why laptops have two hinges -- when one is dead, the other one can continue to hold the LCD monitor to up-right position.
Unless the other one snapped as well.
Two weeks ago I was typing something on my laptop, and there went another "SNAP!" the left hinge broke as well! It sucks to have both hinges broken, because the LCD screen can no longer stand by itself. It either falls flat to the back and knocks something over, or falls to the front, closes the computer, and puts the whole thing into hibernation. I have to use a book-block to hold the monitor while I am typing.
No good. Especially when it is already out of warranty.
However when I googled around, broken hinges on Dell Latitude D6xx models are actually pretty common. Moreover, it is also trivial to find replacement hinges on eBay. So instead of throwing out this perfectly fine laptop, I went and ordered a pair of hinges for USD$22 delivered. It came today, so I got a chance to put them on tonight.
Getting hinges replaced is pretty trivial -- basically just open up the cover of Latitude's LCD monitor, take the old hinges out, and put the new ones back in. A few screws need to be unscrewed/screw back in along the process.
Now it is back to life again with the new hinges, so LCD screen no longer requires external support.