Happy to help.... it sounds like that card worked up to some recent date, and then started going downhill. Assuming you have not changed its slot position then it should still be doing fine.
That is a 40W max card.... and does not have a power plug to receive supplemental power. The video PCIe slots in that workstation are the very top one, and the one a few down that also has the special green plastic catch that locks in all PCIe video cards. It is in the manual.... the upper one has more capability, but the lower one has worked great for us also.
That lower slot can only provide 25 watts up to the card, so that is not the place to put it because it cannot receive more power (75W more) from the supplemental PCIe power cord that you can get from behind the power supply. The upper slot can provide 52 watts, so that can handle the draw of that card. If that is where it is and it is failing there then time to get the cards I mention, in my opinion.
There are other ways to run 4 monitors, but this is what I know has served us very well for several years now.