Getting NO Video

[Ramtrap]

I have a roughly 4 or 5 year old computer hooked up in my living room to the tv. Every now and then the fan buzzes a little loud so I gently tap the side of the box with a remote. Sometimes it'll lock up. Keep in mind this is a gentle tap just to get the fan to chill out.

A couple days ago, that tap locked up the computer so I rebooted. No video. I've tried:
Rebooting again
Completely cleaning/air-dusting
Re-seating video card
Connected a new DVI to HDMI
Hooked up thru VGA
Bought a new video card assuming it may have died (Radeon HD 6570)
...nothing has worked

I guess I'm asking the community here if there are other diagnostics I can do to attempt to get video to pop up. I don't think it's a power or monitor issue because my tv will only show active inputs. i.e. when my PS3 is off, I'm unable to select that input. Same story here: when the computer is off, I have no selectable input, but when it's powered on, the input on the tv is available. That alone makes me believe there's an attempt being made by the computer to push the video signal out, right?

Could it be just a blown motherboard or the graphics card slot is jacked? Any other tests you would recommend I try?

Thanks,
Will

 

[Ramtrap]

Additionally, this is the motherboard (MS-7548):
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&dlc=en&docname=c01635688

I have no idea to tell what processor I'm using.

*EDIT*
I've also confirmed it's not the CMOS battery. Tried the onboard (which I have no idea if it ever worked...had a tab on it that said DO NOT REMOVE, but there's onboard VGA and DVI), and those don't work either. It's GOTTA be a shot motherboard, right? lol

Just wanna know anything else I may try before I buy the motherboard since it's a $200 experiment if that fails. Or...I guess I could just rebuild, huh....yeah, that's me, thinking and typing in real time....

 

[maxinexus]

The only suggestion I can give is to blow up all the dust out of your 5 year old pc and try again you video if it does not work your MB is at fault.