how do I fix my toshiba laptot 9100? when i reboot it goes thru everything normally but when it goes to windows the screen is black. need help!

try to hook up an external monitor check if it will work normally..or try booting to safe mode check if you will have a display...

Try booting into safe mode by hitting F8
If you are able to get into safe mode
right click my computer
select properties
Select the Hardware tab
then select device manager
go to display adapter click on the + sign right click the video card and click uninstall.
Then restart your computer.
When you restart windows should go through because the display drivers are not installed and it is using generic drivers that are used by windows. What may have happened is that the drivers for your display may have gotten corrupted or conflicting with another device this what usually happens when this accuses hopefully this should work and windows will reinstall your original drivers back.