I just received a Raidmax Sagitta 2 computer case. The case came with a 450 watt PSU. I connected three fans to the coressponding PSU molex connections. I attached the PSU power cord to the PSU. Then I turned on the PSU power switch expecting the fans to work. Although nothing happened. Do I need to have the motherboard installed to get the PSU to power the Fans?
Short answer - yes, you need a motherboard to activate the powersupply.
Long answer - it is possible to short out two wires in the 24 pin header cable to turn the power supply on. Its recommended for testing purposes only and should not be used for any period of time as there is no load on the PSU. (three fans doesn't count)
Google to be sure but it should be the green wire and any black wire in the 24pin connector. A paperclip or other jumper wire can be used, just be careful not to jump the wrong wires, and again - THIS IS ONLY FOR SHORT TERM USE. You have been warned.