Galaxy GT 250 -- no video

I installed a galaxy gt 520 on my gateway dx4200 and after install i had no picture thought maybe i had to disable onboard gpu so i powered down unplugged and plugged back into on board slot and now i have no video at all? what possibly could be going on
 
it says the minimum is 300w power supply and that is what i have could i just need a larger one? i am still dumb founded about why i am now getting no video with the card taken out
 
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