there is also the possibility that the setting is not right on the ps3. try connecting it to your tv via scart first. if it works, then the setting is on scart connection. if it doesnt, then its on HDMI setting. best thing is to turn the console on, (when its connected via scart) and hold the power button for 5 seconds. this resets the settings to their basic factory settings.
when you have done this, power it off, connect it via HDMI to your monitor, and you should get a message saying that a new HDMI connection has been deteccted, and would you like to upgrade to this setting? say yes and it should work.