Hi,
How can i turn on the computer power supply uotside computer to use it multi range voltage in other applications like power supply for bread board and so on.
If is is a modern power supply, you can surely use the 5V standby supply. If you know how to turn on the PSU (modern PSUs need a signal to turn on), you can use all voltages. With older PSUs you can use all voltages without the need of a signal to turn on the PSU.
I did something quite similar for my supply. Works great for logic, but needs filtering for use with analog circuits.
Note that most ATX supplies don't provide much current on the -5V and -12V outputs, usually under 0.8A for both combined. That's because the only place it's used is the RS-232 communication ports, which will likely go away in the future.
For computer SMPS units it is great and available very cheap .The trick is you have to permenantly put a load on the 5 volts output (like a lamp load between black wire and red wire) to get all voltages on the output .
the ATX need to make a bridge between two wires in it's output socket ( in the middle with colors green and black if I still remebre it please revise it