Likely either the PSU croaked *happens all the time* or the mobo power modulators or capacitors finally gave out. If you have a spare PSU lying around with the proper connections, you could try to power it up that way. If that doesn't work, its pretty DOA.

Easiest thing to do is just simply slap the old HDD as a slave in another desktop, boot up to its Windows OS, drill through the old HDD and copy the data you need over. Did this all the time at my first IT job years ago. If the settings wern't changed for the outlook express, they will be stored in a default location.

Windows 98
C:\Windows\Application Data\Outlook Express\(GUID)
or

Windows XP, 2000
C:\Documents and Settings\\Local Settings\Application Data\Identities\(GUID)\Microsoft\Outlook Express ---------

To find your address book, do a file search for a *.WAB file as it may be in several locations depending on the OS and how it was set up

Thats the simpliest way to do it