I have replaced the power supply and the new onedoes work but the computer will still not
power up. I desperately need information that is on it. The day it shut down the keyboard didn't work, but mouse did when I tried to repower nothing. E-machines said that it was power supply which I replaced. Any suggestions.

This one is as broad as it is long on the information provided so far. We need to know the following:

When you try and boot up, does nothing at all work? No fans, no lights, no disk whirring? dead and silent?

Obvious question but still needs answering - the switch (if any) at the rear of your PC is on?

When you first tried the new POSU, was there any noise, clunk, flash? Anything?

Are you in a position to put a voltmeter on the outputs of the new PSU?

On experience alone, I doubt that the original PSU blew. Something on the motherboard may have fried and that would result in a line that the PSU looks for not being present and after a moment, nothing happens.

Let us know.

Nothing happens at all when I turn the machine on. The switch at the back is on. When I changed the power source thre wasn't any strange soud , lights or anything. I do notice a very small green light is lit when the power source is turned on. This did not happen with the old one.

I also don't know what a voltmeter is? Sorry I am a complete novice.

The small green light says that the new PSU is functioning.

As I said before, in that case something on the motherboard may have fried and that would result in a voltage line that the PSU looks for, not being present, it stays dead.

This is a case for calling the e-machine people again and making them live up to their responsibilities (if they have any).

A voltmeter is a device that measures the voltage across two charged objects. I don't think this is really necessary unless you know what you are doing really so ignore that. Obvious question but have you plugged the PSU cables back into the motherboard slots where the original cables were?