My screen say no bootable device -- please restart

Oluseun, you did not tell us which Toshiba you have:-) It does sound like either your hard drive has failed, or your have a corrupt OS. Set your Bios to boot order from Optical Drive first and try to start your computer from either a Win start-up Disk or a Live Linux version and see if it lets you access your hard drive. If you find that it does, try to format your Drive, after removing any files you need. If you can not access your drive, you may have to replace it. Hope this helps, good luck