Please help this non techy person get a full screen display on my new Samsung monitor and 13"macbook. I have looked at various other posts but cant find anyone with the same issues...

I have an old (2007) 13" macbook running 10.6.8. I just got a new samsung HD monitor S22B300 and try as I might I can't get the monitor to display with a full screen. I have large black strips to the left and right and the display quality is not that great. BUT the really freaky thing is that the other morning after powering everything down and then turning on from one power source I got a beautiful, full display. When I looked at the Display preferences drop down (I have it in my top menu bar) it showed only the monitor as a screen and did not list the color LCD details. That was the only difference in the settings. I hadnt changed anything.

Have not been able to replicate since. The guys in the Apple store are frankly not interested. Have been in three times and first time was told that if I make my display 1080p it will all work fine. It doesn;t. Second one said I should set the monitor resolution to 1:1 but there is no option to do that on the monitor settings. Third one today said it just depends what order you turn things on. Have tried every variation i can but nothing works. They did tell me I was using the correct adaptor and HDMI cable.

Arrrrggghhhhh... Oh and my hard drive on the mac went yesterday so am losing the will to live....There must be someone out there who can help me!!!!