Computer hardware help

[Grog]

I have a hand-built computer which had worked fine for months. I accidentally screwed my master boot record up by deleting an old Ubuntu partition and ended up fixing it by doing a clean install of Vista x64 over XP Pro. I can't recall what incited this, but the computer started to not "turn off" after I shut it down. To be more specific, I select "shut down" in Windows, the screen progresses to blank, the monitor turns to its idle-off... and everything else seems to keep running. The CPU fan runs, the case fan runs, the power light is on. Of note, the DVD drive will not open and does not seem to spin and I think I think I've heard the hard drive spin down as well. The power button still "turns it on" by starting the boot sequence and the normal startup beeps. This *may* have coincided with me sticking my old DVD drive into this new case (I had planned on putting a Blu-ray drive in this new build, but ended up just going drive-less for a while do to financial constraints), which may have ended in me mucking things up accidentally.

The only thing that turns everything off is pulling the AC plug. I'm pretty sure that when this first started I was able to pull the plug for 10 seconds or so and then plug it back in and it would stay off, but it definitely just goes into that not-on, not-off state if I do that now. I've been really busy and haven't had time to fool with it, but the other day I reset the BIOS to default and deleted Vista/installed XP again with no effect. I would really rather not tear everything out and put it back in if that won't help things.

...help?

[AGS]

Does this behaviour hold true if you:

1 Try a shutdown from Linux (i.e. Ubuntu)
2 Try a restart from software from either Ubuntu/Winxp?
3 Hold in the power button to force a poweroff
4 Press the reset button

If:

1 Shutdown from Linux works but not Windows - Reinstall MB drivers, if it doesn't work from either look for loose cable, or BIOS settings.
2 If it works from Ubunti but not Windows - MB Drivers again, if it doesn't work from either loose cable and/or BIOS settings
3 If it works cable is fine and we are back to software - but then it SHOULD be Windows specific. It could also point to settings in the OS.
4 If reset button has no effect back to hardware.

Yep you don't want to do PC troubleshooting as a dayjob...