You have to be clearer for us to be able to help you mate. If you're stuck in a bootloop, you can simply boot into the recovery of your device and do a factory reset and also do a wipe of cache partition. If you somehow have screwed up your OS, you can flash in the factory images by searching for them online (Hint: It will be a Google page)
You will require Android SDK installed on your computer. Just click flash-all.bat if you're using windows to get started after downloading and extracting the downloaded file.