You should first plug in an External monitor to see if the problem is with the actual Monitor or the Video Card. But no matter what here the Maker or their Authorized Service Agent needs to repair this problem. Look here on the Toshiba Web Site for your nearest Service Agent.
http://uk.computers.toshiba-europe.com/
But before you send it away you need to Backup all of your Data. The repairers will reimage the HDD most likely so any Data on it will be destroyed. Remember to include your Address Book and any E-Mail that is Stored on the computer when you backup your Data.
Col