Login to account, etc problems

Hi,

I installed wordpress on my site via my host, straight onto the root folder of httpdocs of my site.

I go to http://www.mydomainname.com/install.php afterwards, but of course, it was already installed. I click on login on my page and I can login to my dashboard, but then when I click on my account, or any other link, this message comes up:

You do not have sufficient permissions to access this page.

I have NO idea why. I keep putting in the correct login details.

Please help. My knowledge of WP is very limited.

Kind regards,
Diana