Suffice to say it won't turn on.
If it is a desktop and it won't turn on it is more than likely the PSU. You can pick them up for pennies (unless it's a Dell Dimension c521
) and they are easier to fit than counting to 10. It is worth trying before you shell out as there is virtually no outlay. PM me if you need assistance.
If it is a laptop then it could be a host of things but 95% of the time I have bumped into that problem, it has ended up being the mobo