Re-uprading to Win 10.

There could be a few reasons why you're encountering difficulties installing Windows 10 on your Toshiba laptop. Here are a few things to consider:
1. Compatibility: First and foremost, you should ensure that your Toshiba laptop meets the minimum system requirements for Windows 10. Check the official Microsoft website for the specific requirements, including processor speed, RAM, and available storage.
2. Licensing: Did you purchase the correct version of Windows 10? Ensure that you've bought the appropriate license, as there are different editions available, such as Home, Pro, and Enterprise. Make sure the key you received matches the edition you intend to install.
3. Activation: If you previously upgraded to Windows 10 from Windows 8.1 and then rolled back to 8.1, your laptop might have been registered with Microsoft's activation servers as having converted to Windows 10. In this case, you may need to contact Microsoft support to reactivate your license.
4. Installation media: Sometimes, the installation media you are using can cause issues. Try using a bootable USB or DVD created using the official Windows 10 Media Creation Tool, available on Microsoft's website. This tool will create installation media specifically designed for Windows 10.
5. BIOS/UEFI settings: Check your laptop's BIOS or UEFI settings to ensure they are properly configured. Make sure your BIOS is up to date as well, as outdated versions can sometimes cause compatibility issues.
6. Device drivers: Ensure you have the latest device drivers installed for your Toshiba laptop. Outdated drivers can cause conflicts during installation. Visit the Toshiba website and download the latest drivers for your specific model.
If you've checked all the above points and are still having trouble, it might be helpful to provide more information about the specific error message or issue you are encountering during the installation process.