I have similar issue, after shutdown when the system is turn on again, it logs in with decreased resolution like 1200x1024 instead of 1680x1050. Installed latest driver from nvidia, have no idea what could be the reason.
Cpu: Intel E6600
Ram: 2 x 2 GB ddr2 1066
Vga: Zotac 560 ti amp
Psu: Cooler master extreme 380W
Could it be that your old PC has a lower resolution and different aspect ratio that the new one... Try this... watch a Youtube Video in HD in full screen and if its clear then the source of the videos that you have is bad. If its still unclear go and check your HDCP status in the nVidia Control Panal
I am having the same problem with this card zotac gtx560ti and hdmi.
The resolution is fit to screen if i choose dvi. but when i choose hdmi, the resolution gets wider and blurry though its still 1920x1280. The text is also not clear. I have lg 23" wise screen with full hdmi support. I got this card today.