I reinstall my windows, my harddisk got formatted
Can i recover the Extension?
I don't have the private key
There are no extensions for Myetherwallet. Are you talking about MetaMask? if yes, there are 2 ways to recover your wallet. If you have saved seed words and password, you can log MetaMask wallet and if you have your private keys, you can import them into the new one. If you are talking about Myetherwallet, you can log with using your private keys or keystore file and password. If you lost all, there are no ways to recover your ether wallet.