Can anyone properly diagnose this computer problem?

[mtd15us]

So, when I turn on my pc it displays no video or audio, the fans all run loudly even on the PSU and the GPU, a yellow led is lit on the motherboard, a red one on the GPU and green on the back of the PSU. It isn't giving me any beep codes at all, and I've already tested for a bad PSU by unplugging everything and then plugging back in one at a time, no luck. This is a Dell XPS 630i with an ATI 4070 512mb card, a 750 watt PSU, a quad core processor running at 3.1 ghz and the factory installed motherboard (I don't have the exact board specs but if you need them I can get them) and 8 gb ram. I keep getting info about a bad PSU but I'm not so sure because I'm not getting any results that would lead me to believe that that is the problem. Unfortunately, my board is worth about $500.00 and the processor isn't exactly cheap either. On top of that the cheapest repair guy in town charges $70.00 an hour, that's twice as much as my mechanic and about $30.00 less than my lawyer which is ridiculous because I can do most of what he does myself. The three main problems that I understand that this could be are the PSU, the board or the processor. These are all very different problems cost wise and the lack of a proper diagnosis is causing me to avoid making the decision to move forward. If you know your tech then please help me out. If you just have an opinion then try YT, FB, Twitter or Tumblr. Thanks in advance.
OMFG, go to hell muhammed you stupid troll!

Jain and Esta, please don't post an answer if you don't know what you are talking about or if you can't bother to read the question. I can't run a diagnostic or hit F12 because the computer displays nothing when it starts.

Ken, thank you I will check it out and if nobody else gives a better answer before time runs up then it's yours. I appreciate that you know what you are talking about and I wish more people would follow your example.

[Rishabh Jain]

Well try the DELL diagnostic tool, well when you computer restarts press F12 continuously and the the last option is the diagnostic one, just try using that it will scan your computer and search for the problem.

[Muhammed]

here you may get some help
http://bestwebpost.weebly.com

[Esta]

You can first try diagnostic tool to find the solution.If it is not resolved then you should try to get some reliable service at Milwaukee.You should see for on-site and in-store check for your computer. You can either bring your machine into one of reliable to provide you support on the site or remotely.

[Ken]

No POST Beep indicates either PSU or Motherboard ( usually )
I wrote a tutorial on this ....see #5 in Hardware in the link below
http://www.freepchelp.co.uk/threads/1584...0JpNSCShx0

There is also a tutorial on testing a PSU - #3 i Hardware

Try removing the RAM and put just one back.
It will run OK on one module.
Try the other by itself if no luck with the first one.

You can also try taking the mounting screws from the motherboard and sit this on a piece of card or newspaper. This will insulate it from the case.
Try booting up now.
If it does boot you had a short between the motherboard and the case.

Hope this helps.