Hardware fault if rebooting ? Found this.

Change c807, you can also replace C807 220uF 16v with a new 330uF 16v on the motherboard

It can be bought in almost any electronic parts store
and it costs less than a euro for the best.
Replacement still needs to make someone who understands even a little in electronics.

See first and second image,

For those whose duo is still not working after replacing c807 here is the solution.

See third image,

If you don't change c807 on time, and if you play and experiment with bricked duo with power switched on, the regulator (No3 on photo) will die. On duo it's marked Pz 1021ai and universal name isAOZ1212, there are 3 exactly the same regulators on duo (see photo), but note that all are outputing different voltages, this is from memory (measure before changing anything):
1. gives 2.5v
2. gives 1.25v
3. gives 1.15v

If you can find a spare (which is extremely difficult) just replace it and duo will work like new.

And if no spare is available don't worry there is a solution. Here is what we did:
We found manual schematic for DIY regulator that converts 5v to 1.25, and we made it
Took out the working regulator from position 2 on photo and istalled it into position 3 in place of defect regulator.
We manualy injected 1.25v from theDIY regulator directly into the output pins of 2nd regulator and whouala the DUO works like new.

Now the cause of this is simple, prolonged exposure to heat makes condensator c807 break, which can than break regulator. The position of c807 is very near HDD which creates heat especially if used extensively. Or if you have fan problems this can reduce the amount of air circulating which can be also cause. Or simply the batch of condensers used in some duo mainboards is not so good. In my case, it was after 2 and a half years of extensive use. And the new condenser costs just 5eurocents and the regulator costs 1 euro.

TS

P.S.: Go to Johnny Topic about this problem

All the best about hardware/support from Johnny_B, link :
http://jb8a8f8.com
http://jb8a8f8.nl

and on PSU, C14 e C15 to replace

1500uF 10V 105°