Power cords - AC input and DC output are not as robust as you may think - if the wires inside are stretched by tugging or tight coiling-up the inner conductors will eventually break (open circuit) - common also on headset wires and vacuum cleaners.
Get yourself a new power cord and work out a storage technique that does not strain the cable - my guess is that it will never ever fail if you treat it right. Avoid tight bends.
How can I say this?
Over time I have diagnosed two or three dozen faults where inner wires have snapped inside the cable at the bend point - my guess is just based on repeated experience nothing more.
My Dell power cords are fine and have never failed (yet) - a total of perhaps 10 years between the four Dell adapters in the house.
I hate it when it happens to me - I have to fix it - so I fight against it and give pompous instruction to wife & son. Nautical style coiling-up may be your long-term solution.
Good luck...
Peccavi
March 2010