Shalom Attilio,
Not a DBA but highly experience with Oracle "nariskait" which roughly translates as silly behavior.
Try logging on to the database as the oracle OS user. Go for dba priveledges if possible.
shutdown immediate
If that does not work
shutdown abort
That WILL work
startup
shutdown
Now you may restart.
If you can't get the database to behave nicely go ahead and restart the server. My steps increase the liklihood of a clean shutdown/start and lower the liklihood of data corruption.
Normally the database will recover after boot anyway.
SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com