Changed Motherboards, No Screen

Hey there,
I have a problem with my computer and I was wondering if anyone had a solution.

First off, a while back I purchased a Abit A-N78HD Motherboard and put it into my pc. At the time I had a 450watt power supply, when I plugged it in it resulted in blowing my Power Supply and what I was not sure about was whether or not it took the motherboard with it.
I then purchased a 550watt power supply hooked it all up and nothing happened. Therefore I guessed It blew my Motherboard with it.

Meanwhile I Purchased a newer computer, not great but all new parts.
This included:
- AMD Athlon x2 5000+ DualCore
- Corsair VS2GBKIT667D2 D/C DDR2
- GF7050M-M nVidia MicroATX AM2
- CG 450w ATX 24p now upgraded to Vantec 550w
- GeForce 9800GT

The rest irrevelant.
What happened was I was curious to see if the Abit Motherboard was 'really' dead or if I hadn't plugged it in properly several months ago. So I changed all the current part in the computer into the Abit Motherboard, again nothing happened.

I then gave up trying, turned the computer on and off, nothing happened so I moved all the other parts back onto my GF7050M-M Motherboard and turned on the PC...

The computer itself turned on, but nothing came onto the screen.

I TRIED THIS:
Checked all the connections, graphics card, ram, cpu, power etc.
The graphics card was properly inserted to power and the motherboard.

I just don't know what else to try, I'm sort of new to all of this and am unaware of what other things it could be.

Anyone have any solutions?

Thanks

Tangles_101

yeah, i tried both of the dvi slots in the back of my graphics card and the m/b
the screen doesn't come up. all i did was switched the m/bs around and the switched back. plugged in the main 24 pin power, 4 pin power, the cpu fan, graphics card, ram, cpu, case power pins, audio pins, and HDD sata slots...