I reinstalled piwik after migrating from a shared to dedicated server. I went thru the entire Piwik setup instructions and selected to have the "old" database files deleted and reinstalled with new tables.
I added the first website and got the tracking code.
Now Im trying to login again, enter username and password, click Sign In and it just erases my username and password.
I dont even get an error message. It just continues to do this everytime i try
Now I am getting this and my cookies are enabled:
Error: Form security failed. Please reload the form and check that your cookies are enabled. If you use a proxy server, you must configure Piwik to accept the proxy header that forwards the Host header. Also, check that your Referer header is sent correctly.
Are you using piwik behind a proxy? try with a different browser maybe?
I had the same problem. In my case it worked again after I commmented session_save_handler = "dbtable" so it saves in filesystem (default) again. After that I could login again without problems.
Also see http://forum.piwik.org/read.php?2,75338,page=1#msg-75522