my emachines 620 will not power up,where do i start?

Bin it and buy a new computer.

Emachines are very well known for being extremely poor quality.
The PSU usually goes then it does serious damage to the motherboard.
There are tens of thousands of them clogging up landfill sites across the world right now.

while i dont disagree with anything on rik's post I would at least think about replacing the psu (relatively cheap) before binning the whole computer.

Your local computer shop will be able to provide you with a suitable one for not very much money

A majority of people that have tried that before have ended up with a second dead PSU as the damage that is usually done to the mobo causes damage to any other PSU that is plugged into it.

I agree that is a possiblity

Its a gamble - ultimately the emachines as you say were a poor quality machine - but is it worth a £20 PSU against going out and spending £100's on a new machine if there is a possiblity (albeit a smallish one) that it might work.

I personally would take that chance - you apparently would not - it is upto the original poster to decide for himself whether or not he wishes to do so - as long as he has all the information on which to base a decisiong - which you have provided.

As i said in my original post - I dont disagree with anything you have said - I just suggest a slightly possibly cheaper alternative - although again as you say it may be money down the drain.

I understand where you are coming from and if it had been any other make of pc then I would have suggested exactly what you have. :)

I have only ever managed to get 1 failed emachine going again with a new PSU. That's out of more than 15.

lol, them is not good PC's. :)