Trouble in my head

I have a 15" CRT monitor runs my amd monster, then i borrowed my friends 19" Flat screen it worked very well but when i plugged my 15"CRT back it bootes and load then you hear the Vista login sound but the screen goes BLACK. I have another a different pc but the screen wotks well on the spare PC that i did not use on the 19"flat screen. I tried to boot on safe mode but i cant go in. Maybe i'm too DUMM for my own pc...i'm suppose to develop a cul game.

Mainboard: Asus
OS: XP: 5.1
AMD athlonxp
ThanksTry starting in Safe mode and then checking your display settings. Yah it could be the display settings are out of range for the old 15 incher. In safe mode the display settings are defaulted so if you can see it in safe mode that is the problem otherwise it would be a GREAT REASON to UPGRADE!!How do i get into safe mode?
But it works ok with my spare computer.When the computer is booting up hit F5 it will bring up a list of options towards the top will be safe mode.More LIKELY, it's F8.dar you are right