Electronics 2000

Hello
Please could some one help I am trying to make a desk top power supply from a pc power supply but I can only get 5v the rest of the colours like yellow at 12v do not work.
Thank you for any help, Bill

Have you shorted the green wire to any black on the 20/24 Pin ATX connector to turn the power supply on?

The +5V you are measuring is probably the +5VSB rail that's present all the time.

If it still doesn't work it may need a small load on the +12V rail, a HDD usual does the job.