Burning smell for my computer

[Dominatetrix]

I noticed a couple of days ago that i smelt a light burning smell in my bedroom almost like a candle was blown out, couldnt find the source and it went away fairly fast.
Well later that night I went to turn on my pc and the light came on for just 2 seconds and powered off and the green light was on, on the psu unit.
but didnt stay lit long.
So everyone said Psu got a new one installed today and now the pc powers on and after 10 seconds all the fams but the psu fan shut off. the monitor powers on but no display and the keyboard powers on and lights up just shuts off within 2 seconds.
The ethernet cable in the back is not lit up.

Can i please get some help in finding out whats wrong
This girl is so distressed about this and sick of spending money on the wrong fixes.
Thanks

HP Pavilion a6720f (Phenom X4 9950 2.2 GHz)
Overview User reviewsSpecsPart Number:0884420456179.General
Platform Technology AMD LIVE! .Type Personal computer .Recommended Use Home use .Product Form Factor Tower .Width 6.9 in .Depth 16.3 in .Height 15.2 in .Localization English / United States .Desktop type Budget desktop system .Processor
Type AMD Phenom X4 9950 / 2.2 GHz .64-bit Computing Yes .Installed Qty 1.0 .Max Supported Qty 1.0 .Cache Memory
Installed Size 2.0 MB .Cache Per Processor 2 MB .RAM
Installed Size 6.0 GB / 16.0 GB (max) .Technology DDR2 SDRAM .Memory Speed 800.0 MHz .Memory Specification Compliance PC2-6400 .Form Factor DIMM 240-pin .Configuration Features 2 x 1 GB + 2 x 2 GB .Storage Controller
Type 1.0 x Serial ATA - Integrated .Storage Controller (2nd)

comp specs
it was upgraded to a 250gt video card 6 months ago

 

[davcon]

I would check the motherboard for faulty capacitors.
If any are bulged(not flat) on top you have a bad cap.
http://www.google.ca/search?hl=en&sugexp=kjrmc&cp=15&gs_id=1s&xhr=t&q=bad+computer+capacitors&gs_sm=&gs_upl=&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1920&bih=908&wrapid=tljp1318917383131030&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi
I'll bet that's what the problem is.
If that's what turns out to be the problem it's usually cheaper to buy a new board.
That may not be the case in your situation though since it's an oem board.
HP will want an arm and a leg for it probably.
Another thing to try is another wall outlet.
However i still believe your board is toast.
Have you double checked your connections?
Like hdd led, pw switch, reset, and p led
If they aren't correct the board won't power on.
http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&lang=en&product=3970023&docname=c01742903#N1370