Hi Guys!
How can i use old and useless parts of a computer in the field of electronic and robotics ...( All of the parts except the motherboard and monitor.) ??
However i should gave it free to someone or sold it much lower price ...
Are the Computer parts used in these fields?
Thanks a lot.

I guess it depends on what you are trying to build. I salvage parts off of boards all the time. You can get all kinds of neat stuff off pcbs, especially power supplies. Motherboards usually have too many tiny components for the average shmoe to use. You can pull motors off of printers and use that for steppers etc.

If the computer is running and not too ancient you could donate it to your favorite charity.

PC power supplies can be modified to give different output currents/voltages...

Assuming you have the competance to do it...

I save the fine wire used to connect the PCB to the front indicators. The .1 pitch connectors they used can also be recycled.

The power supplies often have some neat torroidal inductors and transformers. I've seen some high-quality home brew switching power supplies that use them.