Nvidia gtx 560 DirectCU screen flicker and pc crash

Screen flickers when i turn my PC on and when i watch videos,flicker mostly ends with a "Display driver has stopped working and has recovered.",or sometimes with a restart..It's really annoying.My driversa re 270.48(clean installed)
on the PSU it says 340w so 340w it is
 
Minimum recommended PSU by Nvidia is a 450 W unit.
Saying that the one you have is 340 W really does nothing, what counts is the amps it delivers on the 12V rail, and that is why we need to know exactly what model it is you have.

You can try and reseat the card (take it out and put it back in, might not be perfectly slotted) but in all likelihood your PSU does not have the amps to power the card.