My computer only shows blank screeen after changing its case. why?

Yesterday, I decided to change my power supply because its fan stopped working. So I bought a new one and connected to my computer. However, because my computer is SONY VAIO PCV RX-450, I could not put my standard ATX power supply in its case. So I immediately brought my old computer case from the garage, and put the VAIO components in there. When I put the switch on, it was just black and nothing else! It does not even show “cannot find input signal” No, it just shows black screen. I tried various methods

I….

1.pulled the monitor plug and connected again

2.pull all PCI card and put the power on to see whether they are causing problem

3.reconnected my ram

4.reconnected power supply wires

5.brought my old power supply and connected to the computer again

My old power supply was

delta DPS-150bb-1b power supply

And I used this for my new power supply

MADDOG surepower 250w

http://www.mdmm.com/products/techietoyz/...

any way to fix this?

My computer only shows blank screeen after changing its case. why?movie theater

pull the motherboard out of the case and set it up on a nonconductive surface, put in the video card and plug it in. if it doesn't power up you may have shorted the board.

My computer only shows blank screeen after changing its case. why?tickets opera theater

Have you tried putting everything back the way it was when it was functioning? If that makes it work again then one option would be to simply replace the bad fan that was in the original power supply - just make sure it's completely disconnected from A/C power before you open it up.... Just a thought - what may be causing your current 'black screen' is an extra metal stand-off touching the underside of the Sony motherboard that's mounted in your old computer case. You could also try running the motherboard outside of the case. Good luck.