A power supply not being able to supply enough voltage to the graphics card or the graphics card itself going out could be the issue.
The Chieftec GPS-600A8 power supply only has an 80+ rating which means it just barely meets the qualification of being a functional power supply.
If you end up having to replace the power supply I would recommend going with something with an 80+ Gold or higher rating, such as the Corsair RM650.
A dying power supply can take other other parts or even the entire computer down with it.
I would start with testing/replacing the power supply and moving on to the graphics card after you have ruled the power supply out.
I would still keep the new power supply even if it does end up being a faulty Geforce 950 .... my Geforce 970 died on me last year