Is something folk are rarely ready for. This could be too many things from a bad AC cord, power supply to just a bum on/off switch.
While it would be nice to get someone to walk you though each test you have to have some basic repair skills or use google to figure out what is what and how to test each part.
Hope it's a simple thing like no power.
i have a 2005 HP desktop media edition xp.. and i shut it down the other nite and next morning, it wouldn't do anything.. no lights or sound. is it the power supply? was workin fine when i shut it down.