Help, my brethern, I need it

Question

Howdy all. I have a bit of a problem with my HTPC.
I have a custom built HTPC that refuses to display video. It's an HTPC case, with an MSI board, Intel C2D 2.0GHz, 4GB DDR2 RAM, 500GB HDD, GeForce GT 220 gfx, 500watt PSU, and a DVD RW.
The problem is that although it will power on, I cannot get it to output video to the receiver. I know it's setup correctly as it was an intermittent problem up until a few weeks ago when it flat out refused to POST. Even when powered off the LAN light stays amber, and I have yet to find anything referencing this on hardware forums.
It's driving me insane, and my girlfriend says fix it or toss it, and I'd rather not lose it. LOL.
I did read online of a possible fix : disconnecting power and switching the voltage selector to 230 for a few seconds, then back and plugging it in. Didn't work.
I'm assuming something has failed, most likely mobo, or PSU, but I can't tell which since it power on, but doesn't POST, so I can't really diagnose further without starting to spend cash(which is tight).
Helpful suggestions appreciated I can post a full list of part numbers if requested.
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Answer 1

I would blame the PSU as it stands right now. Lets look at the facts:
1. Bottom-rung PSU from a relatively no-name brand, rebranded as Apevia(There's about 4 actual manufacturers of PSUs: CWT, FSP, Seasonic and /unknown chinese factory/). I'd be surprised if it could put out 300W under /optimal/ conditions, not that you need it. (*)
2. Computer won't boot, but harddisks spin up. Sounds to me like, say, the 3.3V rail or one of the other low-voltage rails for the main system failed, but not the 12V rail that supplies the harddisks. Most drives will spin up with power, even if they aren't connected to anything data-wise.
My solution? Buy yourself a new PSU(preferably from a quality brand like Corsair or Antec). Alternately, yank one from something else you have around, and plug it in. It doesn't *have* to be mounted in the case.
(*) A note about PSUs: As more people built their own machines, and bought expensive, high-wattage power supplies, the chinese vendors realized that almost noone *actually* needs, say, 500W. So, they build them for about 250-300W, label them 400-900W, and sell them for cheap; Most people won't ever run into the limit, and so they can get away with it(Note: ever take apart a Dell or HP system? Note the low wattage on their supply. Also note that those supplies *will* supply what they are rated for, which is why it works).
On top of that, they also cheapen it by reducing components that aren't absolutely critical - using lower quality capacitors to even out the voltage coming out, for instance. This will cause random crashes when you near the actual maximum output of the supply, and other odd glitches.
In your case, you most certainly didn't run into that limit. But you did run into simply having a DoA and or simply something with a weak component, which simply died on you. I would try to find a better quality one - Quality PSUs(which should have the 80+ logo and not cost $20) are both far more efficient, and will keep your system running well for years.