ok i'm trying to fix my friends emachine but i can't seem to found the problem.
i hooked everything up turned on the pc nothing happens so i tested the power supply found out it was the powersupply i changed the powersupply.
now the pc want stay on it would come on for a min and then turn off.i don't think its the powersupply because i test it and it good.to get on back on i have to put the powersupply tester on the powersupply and it come on. now i try to put windows on it ,it will go as far the begening and then its start to blink and blink thats it.

First, ensure the power supply is the correct type (20 or 24 pin, extra four pin connector etc.) and of sufficient wattage to handle all the components. If it will only run with a tester connected, something is wrong. There may be a loose connection on a connector.

Then follow the steps in this article to ensure everything is properly connected and individual components are good. (ie; Connect things one at a time and ensure it boots properly with each component.)

http://www.d-a-l.com/articles/library/34.html