okay...i found something. i think alvin was right when he pointed out that it could be because of /etc/nologin (but i cannot log in as root either)... the thing is, the file is there, and i already deleted it but it always comes back. there also is a /etc/nologin.boot and a script /etc/init.d/rmnologin that schould delete the nologin file...
locate nologin says: /etc/init.d/rmnologin /etc/nologin /etc/nologin.boot /etc/rc2.d/S99rmnologin /etc/rc3.d/S99rmnologin /etc/rc4.d/S99rmnologin /etc/rc5.d/S99rmnologin /lib/security/pam_no_login.so anyone? thanks, vester