This is important information that all computer users, that have had thier computers in service or built between the years 2000 - 2005, like many of those that have posted requesting help. Please read this post, and the following links throughly, and examine your system board and all the hardware in your system to see if you have the signs
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There is a disticnt possibilty, for computers built between 2000 and early 2005, as I would assume that yours is, and many of the posters, that it has succumb to dust build up, or the more important point of this thread,
Capacitor Plague
Capacitor plauge is a very very unkown problem, that usually only tech people have heard of, but more importantly
It is estimated that between 70-85% of all electronic devices built between those years have !
Here are a few links to back up my claim, and I will continue to explain below for those that are a little on the lazy side to look up that info
Wikipedia entry
A website that I used to repair a few of my systems, (USA Only), and contains information
Google search for capacitor plague, so I dont seem like some raving wierdo
Geek.com post about the subject
Cnet.com article #1
Cnet.com article #2
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OK! Everyone belives me now right? Now I dont look like some guy holding a sandwich board, standing on the corner of a busy street, yelling that the Lords of Agaroth are coming to spin us all into a garbage can filled with cream cheese & toothpicks!

(I hope)
Incase you did not look at the links, Capacitor Plague is world wide, where "Plague" = super spread problem all over the globe, and "Capacitor" = very vital electronic part that contains charges to be released in timed bursts to other components.
Here is an example of a healthy capacitor :
Oobby
And here is a few bad ones:
Dooby
Review the websites I linked to see if you have fallen to the plague.
Do not think that "Im cool, I dont need to wear protection baby!" .. ... I mean, "Im cool, I probabbly dont have it!". Dont fool yourself, the numbers do not lie, and belive it or not the industrys that have produced the faulty capacitors have been under rigirous legal action so severe it would cause even our favorite boss Glint to cry like a 4 year old trapped in a briar-patch o' rattlesnakes! (yee-haw!)
Open your case, and see if this is not the problem for you.
Dont touch anything that looks like the capacitors that the above websites have discribed.
Help others and post if you have had this happen to you. It will help others to realise that they may be at risk.
My suggestion, if this has happened to you, is that you search the web, and pray to god that you can find a guy that has the ka-jo-nez to solder to a 6/8 ply system board to get it back to normal.
As for your other devices, you may not have any luck with anyone doing those, but try to see if you can find anyone.
If this is your problem, and all else fails, your only recourse is to purchase a new system.
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I thought that due to the response to this thread, and the age of many of the hardware suggested, that this may be relevant.
I hope that gave a little insight, and good luck!