What OS are you using?
bttt
are you logged in?
just joking- if you can reboot in safe mode then you are halfway to fixing it. - what did you do recently to change the configuration of the computer? anything? we need much mor einformation than a black screen
See if it will let you boot into the last good configuration. A system restore, given your circumstance, may be another workable option.
save your data...
IN SAFE MODE
right click on START
Left click on Explore
Drag and drop files or folders onto your CD-R drive
then double click on the CD-R drive
Right click on an empty area of the files list (right side of screen) and select "Record Now."
This will work in Win XP in Safe Mode.
Once you have your critical data backed up, reinstall windows.
What is the brand and model of your computer?