While it could be a security or virus issue which is way back in third or lower places I find that such is usually a driver issue. With a secondary monitor I find most will respond with Huh? when we ask about the secondard monitor driver (aka the monitor.inf file.)
There is no exact fix for this one.
I've got a new build PC. Windows 7 Pro 64 bit, and and nvidia FX4800 using the 311.35 driver.
Everytime I restart me computer my secondary monitor defaults to 1024x768. I cannot change the resolution any higher, only lower down to 800x600. My primary monitor is unaffected by this problem.
If I reinstall the driver it fixes the problem, only to come back after a restart.