After the setup of the FBA site at my own test server I logged on using my client machine (Windows 7) and it worked fine.
Now I try to logon locally on the SharePoint server I cannot select between "Windows Authentication" and "Forms Authentication".
Nothing happens when I click on the down arrow
When I looked at the Sign In window the text looked big and ugly.
Solution: I changed the Zoom-level in Internet Explorer to 100% and login locally works fine!