The Win 8 serial is usually stored in the BIOS, so all you need is an install image. Instructions for finding your key and creating install/recovery image:
http

/dellwindowsreinstallationguide.com/download-microsoft-windows-and-office/download-microsoft-windows/download-windows-8-1-retail-and-oem-iso/
Microsoft site for creating recovery image.
http
/windows.microsoft.com/en-us/windows-8/create-reset-refresh-media
You will have to download drivers for your particular hardware from Toshiba. Most vendors will also mail you a recovery DVD (with drivers pre-included) if you pay for it (usually $10-$25).