Macbook goes to sleep mode for nor reason!!

[Visualgap]

This is very irritating, from time to time when I'm surfing the web or listen to music, viewing photos, etc..., my macbook screen turns black and enters sleep mode! I got it last December, its the 2.2 Ghz white version. Can anyone help me?

p.s : I set settings to "Never" go to sleep mode but it does anyways....

 

[techound1]

Have you reset the SMC? (The System Management Controller is an integrated circuit (computer chip) that is on the logic board of the computer. As the name implies, it is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output as it relates to the computer sleeping.)

1. If the computer is on, turn it off.
2. Disconnect the AC Adapter and remove the computer's battery.
3. Press and hold down the power button for 5 seconds and then release the button.
4. Reconnect the battery and AC Adapter.
5. Press the Power button to restart the computer.