Hi Mohd,
Sorry for not explicitely mention the path of alert<sid>.log file.
If you are using oracle 11g which I suppose you are then the path is as follows:
/oracle/<SID>/saptrace/diag/rdbms/<sid>/<SID>/trace/alert_<SID>.log
Please note you should always refer this log file in cases of errors. It will report any issue if present in the database.
Just like Benjamin said do not kill the TP or R3Trans process. They can cause inconsistency in the system.
Did you check the tablespaces and filesystem for space?
Regards
Robin