Error while opening Oracle 11g Database
Your situation looks most like a powerfailure. This kind can hurt the database badly and in this case it looks like the controlfile or the online logfile is damaged. If you have a backup, start with restoring the controlfile from the backup and recover the database using the backup controlfile option.

With a little luck you can open the database afterwards. With a little bad luck, the damage is in the online redolog in which case you can not open the database in a consistent state. This is because your undo segments are active and they lack to recovery information from the redolog file to recover from that.

Still it is possible to open the database using some tricks but it does require extra work, setting hidden parameters etc. After that type of 'recovery' only export -> create new db -> import is a valid option.