Monitor resol'n overlapping screen at BootUp

Could someone please explain, if they can, why my monitor, during boot-up , has the windows XP logo , covering the whole screen, and... right, lemme try again, my res on xp is 1200 x 1024 , when my PC boots up , it must go to a resoloution that the Screen folds back on itself, top and bottom, and basically, any writing on screen is pressed against the sides of the screen etc. WHEN IT GETS TO THE 'WELCOME' SCREEN - all is okay again ???

I have pressed the 'degauss' on the monitors menu, The monitor is a packard Bell A727 or maybe just a 727 RIGHT - THIS IS NOT A GOOD ECPLANATION OV THE PROBLEM. so .. running my xp - fine - 1200 x 1024 cool boot-up - everything in writing on screen pressed up against sides ov screen and even adjusting the horizontal-size on the monitor buttons it will not allow me to fetch it back on to the screen, i can choose either right side viewing, or go the other way, and move the horizontal to the left, so i can read what's written on the right-side ov the screen. Hope i am making this clear . Just to add, i installed win2000 on another parbreastion, and that , when getting to the welcome screen etc.. AFTER boot-up STILL has the overlapping resoloution-setting

ANY HELP PLEASE - Thanks - Fred