Hello! I have a question regarding my wife's computer.  It is an HP a450n, and recently when trying to power it up the MONITOR, mouse and key board do not show any signs of life except the monitor going into "power save mode" like the computer was turned off.  I sought out some "friendly" ADVICE and replaced the mother board, but that did not fix it.  I also swapped a know good video card & memory into it.  None of the suggestions have worked.  If anyone has any ideas they would be much APPRECIATED.
-WallySounds like a power supply issue. What happened prior to all of this? How old is the machine?

HP's have notoriously small and poorly constructed powere supplies. I think that one is a whopping 250w el cheapo. This is a common problem.

http://forums1.itrc.hp.com/service/forums/bizsupport/questionanswer.do?threadId=961952&admit=-682735245+1169200645352+28353475

Top it all off these are proprietary units, so you can't go to the local computer shop and just buy a PSU off the shelf.The below site has a 310 watt.

http://www.pcpower.com/products/power_supplies/selector/hp-compaq.htmThanks for the info, but I neglected to mention that the first thing I did was swap the PSU out of my PC into hers.  It did nothing.  I'm not the most computer SAVVY person, but the wiring harness out of mine had the exact type of plugs and appear to plug in the exact same way.  Is there an internal difference if the plugs are all the same?
Thanks-
WallyIt's possible...i had this issue with a Dell once. They are wired differently.