hi, well i recently got a 750 w psu, and had a pny geforce 750 1gb ddr5 dual fan gpu.
i hooked up the psu it all worked handy dandy, but when i put the gpu in monitor is black showing no source of display and 10 secs after boot fans slow down, could this be a motherboard issue, or is there not enough watts or even the card is doa??
Did you update to the most recent Bios version for the 620 prior to installing the new video card? The GTX 750 is supposed to run on 300 watt power supplies so a PSU upgrade may not have been necessary. With the 750 watt unit, you have more power than you will ever use. Reseat the video card to be sure it's connected properly and check the cable connection between the video card and your monitor. The 620 is known to have compatibility issues with some video cards so that may be the case. However, I have seen that the GTX 750 did work on the 620, but it was an EVGA brand not PNY. Unfortunately, brand can make a difference since the boards are different.