Hello, i dont know what might be wrong with your monitor but i can help you get into safemode, i assume you can still get into windows and see a little of the desktop.
If you can still see what you doing, edit you boot.ini (C:\boot.ini) this file is hidden, once opened copy the bottom line of code mine looks like this ( multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect ) without brackets then copy it just below the original line instead do it like this ( multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional
backup" /noexecute=optin /fastdetect )
Then goto (>start >run) and type in "msconfig" when it has opened goto to the Tab "BOOT.INI" you will see a label saying "Boot Options" select "/Safeboot", make "timeout" 30 seconds, ok and restart.
This will enable you to enter into you safe mode. The problem why you couldnt enter safe mode before is that you might have a USB mouse or keyboard that is conflicting with it.
So i hope this works for you, goodluck