If you're looking to reinstall Windows Media Center, there are a few things you'll need to do first. Before you get started, make sure you have a backup of all your important files as this process will erase everything on your hard drive.
Once you've backed up your files, the next step is to insert your Windows installation disc into your computer. If you don't have a disc, you can download a Windows ISO from Microsoft's website. Once the disc is inserted, restart your computer and boot from the CD/DVD drive.
When prompted, choose the Custom option and not the Upgrade option. This will ensure that all of your personal files are erased during the process. Follow the prompts and select your hard drive when asked where you want to install Windows. The installation process will now begin and will take some time to complete.
Once Windows has been installed, open the Control Panel and head to Add or Remove Programs. From here, locate Windows Media Center in the list of programs and click on it. Select Uninstall from the menu and follow any prompts that appear.
Now that WMC has been uninstalled, restart your computer once again and insert the Windows Media Center CD/DVD that came with your TV tuner card or other device. Run through the installation process once more and then reboot one final time. That's it! You should now have Windows Media Center up an running again on your system!