login failure without any error message

[pluto]

hi

I am trying to connect to plesk as admin user but I cannot login. There is *no error message* and the login page opens again... There is also no error message when I type the wrong password. A few days before everything was working fine.
I have read a lot of threads in this forum about similar problems but no answer was a help for me. I was also looking in some logs but I found no errors. I also tried to use Firefox instead of IE, what was one hin in several threads, no way.
I am using plesk 7.5.3.

Please help me.
Tnx
pluto