Out of range error

[siddiq1402]

i just installed left 4 dead 1 game by extracting,while I started the game its shows "input signal out of range change setting to 1024x768-60hz,actually my screen resolution also the same i.e 1024x768-60hz but also it gives the out of range error,
but the games strats in backround and the monitor goes to sleep.
what should I do now?
system configuration
core 2 duo 1.86
3gb ram
1gb NVidia GeForce 9400 gt

 

[i7Baby]

legal copy of game?

 

[drixkarasu]

Installed by extracting...
Buy a legal copy of the game and install it properly, then feel free to look for help if it doesn't work.