Damn, that thing must be old, my own one is still running sans the battery which died a little while ago.
In my parents hands now, was a powerful wee thing in it's time but that was like 2004/5 or something.
Have you tried the basic giving it a clean, the rear heatsinks are a terrible one for picking up dust.
Also is that off the wall power, I assume it is but like I say the battery on my own kicked the bucket and has been discarded now.
Does it turn on at all, you say it switches on but does not post. Perhaps it is a BIOS problem, the cmos battery could be going.
It is difficult to tell due to it's age.
Well what I've managed to figure out is that it definitly needs to "warm" up before it posts screen. When I've used it for a few hours and switch it off, then back on again it posts screen normally. But when its cold and first time, it just dosn't boot.
Everything starts, fans etc it just dosn't post screen. Its not the Screen itself either, as I've tried it on an external. It's definitly somthing that needs to be "warmed" up.