Question Is a Nvidia Gt 630 4gb DDR compatible with an Optiplex 755?

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I’ve installed a new graphics onto my Optiplex 755 recently and it was working fine; but today it both screens randomly says ‘no signal’ and the screen goes black. Any suggestions ?

 

[PC Tailor]

If it worked fine before, it will be compatible, it wouldn't work at all if it wasn't compatible.
What is your full system spec including PSU make and model?

Have you tried a different display cable? Are you using any adapters?
Had anything changed before they stopped working?

 

[Hashscreen]

Yeah initially I was using a dvi and vga and then changed it to a vga and hdmi .. but both times it turned black .

Yes I am using an adapter and I’m not sure what the psu is ( am I bit of a noob)