If you are an existing CyberGhost user, please use the menu entry in the upper menu called 'Login'.
Enter your account credentials.
Please log in to an account with a valid active subscription and don't exceed the number of allowed devices.
What could go wrong?
The 'Upgrade' button is still visible: Despite you have logged in with the correct credentials and in the correct account, the client doesn't offer any Premium feature. Most certainly the number of allowed devices is exceeded then, either because CyberGhost had been reinstalled too many times or because too many devices are already bound to this account. Please refer to this article to learn how to free an occupied slot, so the Windows client can flawless connect to the network.
Another possibility might be you entered the credentials of a different account without a subscription. If you have more than one CyberGhost account, please check all credentials for the one, you want to use. Log out from the current account and log in again with the fitting credentials.
No log-in possible: Please check your credentials for spelling errors and try again. If you have forgotten or lost your credentials, please refer to this article to learn how to recover an account.
You don't have any credentials, because you never got them: If you purchased a subscription for mobile devices through an Android or Apple Store, you can't use it as a regular CyberGhost subscription with Windows. It is bound to the account (Google Play Store or Apple Store) you used to purchase.
If you have an activation key (e. g. for a prepaid subscription), it needs to be entered in your account management first. Please refer to this article to learn how to activate a key.