This is not for the faint of heart or if your Raspberry Pi is under warrantee.
 
In my case, I bought 3 Raspberry Pi's from Ebay. Two had damaged UBS Ports and the seller stated that it was unfixable but the Raspberry Pi's can work for projects that do not use the USB ports.

 
Replacing the USB Ports
 
I bought a few spare USB Replacement Ports, and simply put, replaced the ports on the Raspberry Pi's and they now work as normal.

 
Only thing is, the Raspberry Pi's use Raspberry Pi's with Black Plastic Interior, and I got and used USB Ports with White Plastic Interior. Other than the color difference, there no affect on the Raspberry Pi's operation. For me, I can look at the ports and know which Raspberry Pi's from the I own.
 
To do this required a lot of desoldering, and it would be best if one had a desoldering tool like this unit from Radio Shack. Because the Raspberry Pi uses hi-temperature non-lead solder, the desoldering tool is great as to it has a higher temperature to wok with. You also must mix regular solder with the solder on the Raspberry Pi Board to get things flowing before sucking up the solder with the tool. Then the USB Port comes right off.
 
Soldering the new port is simple, but use as little solder as possible, just enough to fill the pin holes while making sure that replacement USB Port is mounted against the board. Do not solder the anchor (large) pins yet. Test the Raspberry Pi, if there is an error while booting that says, "Over voltage on Port 2", then one of the USB Ports has too much solder and has shorted out. Desolder and remove the replacement port as neatly as possible, clean up the board from the excess flux with alcohol and acetone, and resolder the port back in while using less solder than before but enough to fill in the pin holes. Test the Raspberry Pi again and it should be fine at this point. Then solder the anchor pins in place, clean up the board with alcohol and acetone and you're done.

Sometimes your Raspberry Pi is dead through no fault of your own. In this case chances are that it underwent an over voltage condition like a voltage spike or surge and the fuse blew.
 
Replacing the Fuse
 
In actuality the fuse on the Raspberry Pi is a self-healing fuse. When the power going into the Raspberry is to high, the fuse gets hot and then at a certain temperature point becomes non-conductive. Disconnecting the Raspberry Pi from the power source and let it allow to cool down resets the fuse. Once it is cooled down, in lets say an hour or so, you can plug the Raspberry Pi to the power source to turn it on and boot again.
 
But what if so much power went through the fuse and damaged it? Though possible, it is rare for this to happen unless one was careless and tried to feed the Raspberry Pi power from the GPIO. In this case, the fuse will burn out and it needs to be replaced.
 
See these to links about testing the fuse and replacing it:
 
1 - Basic Dead Raspberry Pi Information:
http://www.petervis.com/Raspberry_PI/Raspberry_Pi_Dead/Raspberry_Pi_Dead.html
 
2 - Information about the fuse itself and how to test and replace it:
http://www.petervis.com/Raspberry_PI/Raspberry_Pi_Dead/Raspberry_Pi_Fuse.html

Update to repairing bad voltage regulators on a dead R-Pi.
 
Clarification: This is only for the Model A and Model B which has a linear power supply area, the others use a switching power supply.
 
Since posting this, I repaired the R-Pi Model B in question, but it was tedious because the parts were so small. The main regulator went in with some difficulty as not only are the pins soldered to the board but also its back heatsink area is soldered to the board. It is best to desolder the pins first, and then get the iron as hot as possible and put it on the heatsink until the regulator comes loose and then flick it of. Then use some solder braid to remove the excess solder and clean up the area before soldering in the replacement. The other two regulators were easier but smaller and needs a steady hand to replace them. One of them, the smallest of the two, came out in two pieces so it was obviously defective.
 
With the regulators replaced, the R-Pi runs a lot cooler but still hotter than the others. Something else must have shorted out, but with a heatsink the R-Pi runs normally. I'm thinking of using a Junction Puter (a semi conductor where one side is cold and the other is hot) to cool this R-Pi. As is, I do not dare over clock this unit.
 
Now, what could have caused this? Simple. In researching the R-Pi's weakness, it is the GPIO. In theory, you can power an R-Pi through the 5V/Ground lines on the GPIO. This does work but in doing so you are risking in frying your R-Pi into a crispy chunk of silicon because you are bypassing the voltage regulators and are force-feeding 5V through out the entire board. Many robotic kits connect to this 5V Line, and if the motor voltage supply is not separated, then there is a good change of frying your board. In the Model A and Model B, you fry the regulators first before anything else begins to cook but it will continue to fry the board if left to cook. On the others (Models A+/B+/Pi2), the voltage regulator is bypassed and you immediately fry the CPU. Since this this a Model B, the Regulators were fried first before further damage could hit the board.
 

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Quote from Fernando on Oct 24^th, 2014, 5:05pm:

You should read the posted link: http://www.petervis.com/Raspberry_PI/dead-raspberry-pi/dead-raspberry-pi.html
 
But this is for Model A and Model B, not the Model A+, Model B+, R-Pi2 or R-Pi:0 as these have a switching power supply and not a linear power supply.
 
And the two of the three regulators are really tiny. Don't know how they can handle so much power without breaking? but then again, I did find the smallest one broken when I unsoldered it.

Switching PSUs are great but you then get forced with filtering capacitors all over your board (look at your average PC mobo - LOL!)
 
If you compare the two Model B and Model B+, the B+ has about 2X the filtering caps on it. But the switching PSU keeps it stable, the Linear PSu is all over the place. There's another thread about voltage sensitive R-Pi's and that is also the model B with the Linear PSU. Replacing the regulators fixed it as well.