Computer help?

i have a dell 2400 series computer for 2 years now and i only have one problem with it which developed only a few weeks now it seams that when ever my system is on i have to keep changing the settings on the video of the monitor because the screen would some times move to the left,i then have to bring it back to the center but even when its to the center its not fixed correctly because the edges of the screen where the time and the start menu are located the words,icons are all slanted and smaller than the rest of the page and when i start up the pc it appears all messed up and the the screen slowly starts to pull to the right then all of a sudden the page would disappear with a white flash. the white flash would sometimes fall to the bottom and disappear and leave only darkness but when the start up is complete the screen reappears but its still not the way its suppose to be is it my video card? or is it the monitor? can it be fixed ? pleaze give some advice