cyclone3 nstatus pin keeps dropping low

No, I used to try to configure the device. I can get config done signal with Jtag scheme, and AS scheme is normal too, but device didn't start working. I guess that's because nstatus keeps dropping low, (device keeps on reseting), so there is no valid program downloaded.

So question goes back to why nstatus keeps dropping, even without blaster. That's why I don't think it has any relation with Quartus. (the program we used has been verified well for many times before)

According to handbook, power supply and nconfig could drop down nstatus. I don't know is there any other reason can cause this matter?

thank you!