There may be several reasons that you might lost access to your google analytics account. Some of the reasons might be:
Someone else created the analytics account and now he has left working with you.
Someone else is the admin and he is not giving you the full access
One of your analytics employee resigned and you hang up with the access issue.
Firstly, you have to make sure that you are using the right email account to access your analytics account. A simple option would be creating a new analytics account and link to your site, but this won’t help. You would definitely need your historic data and you would never want to lose it in any case.
The second thing you could do is to contact the admin and ask him to give admin access to analytics account. But if he don’t want to give you admin access or he can’t be reached you can’t do anything with him.
The third option would be reclaiming your analytics account. Once you reclaimed your analytics account, the online support at google analytics will contact you within two business days and further assist you.
If by any means you have lost access to your account and you can’t login to your analytics account, you would need to regain access to your analytics account. You would have to speak to google online specialist, who will ask you questions about site ownership and if Adwords account is linked to your analytics, you would need to answer few more specific questions about Adwords account.