Mysteriously doesn't POST - out of ideas

Here are my settings
A7N8X-VM/400 motherboard
ATI Radeon 7000 64mb agb video card
512 MB of DDR
any other details needed can be provided

This is a weird problem. I was trying to install a second hard drive into my previously perfect working computer when the damn thing didn't POST next time I started Now when the motherboard starts up the keyboard doesn't light up and nothing is shown on the screen. The fans and everything is fine but nothing shows on the screen. I am sure its not the power supply.

These are the things that I have tried: resetted the CMOS
took out the video and hard drive living me with on ly the essentials

also of note:
I did have this same exact problem before but the ONLY THING I did was repadily turn the power on and off and after a while and it would work fine. But now that doesn't work anymore. This is what truly baffles me about this problem. Something very minor is happening that I previously resolved by just messing around with the power on/off.

I would take and unplug all the cable that go to the IDE slots on the motherboard and try it then, unplug everything that the computer wouldn't need to start up, if it comes up, then start pluging things back in till you find the one that cause it not to post. You may try also taking out the cmos battery for a couple minutes, I've found that if you use the jumper to clear it sometimes that it doesn't work

From what you said it is v unlikely that the Hard drive will be the root cause of your problem.
Likely suspects always start with power supply / motherboard..
it may be an idea to remove the motherboard from its casing and hook it up on a properly insulated surface and trying to boot it from there, if it does then it may be that your m/b is being shorted by the chassis..
if that yields no success then try a new power supply if u can.
if none of those get any response your m/b may be at fault, possibly (far reaching conclusion here) a broken printed circuit has been pushed further apart when the 2nd HDD was installed.. if u can RMA it..
easy solution... get someone with a simliar m/b and test all components in there..
hope this helps