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