The first thing I could think is a driver problem but you said you updated.Make sure it is not a BETA version of the nvidia drivers.BUT you re-installed windows so it is not a software problem as it seems.Check the temperature.Also check if 570 is working and you are not working with the sandy bridge graphics chip of your CPU.If it doesnt work the card may be damaged.
Maybe your pc is full of viruses !!! Run pc on safe mode and start Anti-Virus and scan whole pc. I had the same problem, My Warcraft III frame rate is 65-70 on medium - High settings and somehow it starts to lag i lower the settings and still lag !!! I scanned my pc and it found 4 Malawares