I have an ECS NGT520C-1GQK-F (Fermi 520 / 1GB) card that started crashing and doing the windows failure to respond lock-up scenario. Reading around I found maybe half a dozen different reasons and tried eliminating them all - different Nvidia driver versions (now using the latest - but went back to versions from a year or so ago with the same issue). Unplugged my second monitor, checked a bunch of windows settings, etc. Nothing helped. So - I put in an older Nvidia card I had laying around and my PC has been stable. Also - ran memtest and checked all my drives, and ran the intel burn test - everything else is solid. No overclocking, nothing unusual. My PS is at least 500W.
I RMAd the ECS card, and I got the replacement and it does the same thing. I put the older card in, and its rock solid again.
Is this an ECS issue? A Fermi issue? Any thoughts or advice.