CPU is too busy!

 dear all:

             my oracle(10.2.0.3) is installed on unix platform.it's a rac with two node.this week it run properly.

At 10:43 am the cpu of node 2 was used totally by oracle.and the database is not down,but i can't do anything in database such as select * from dba_users....... the same thing accured two weeks ago at almost time. the awr is below:

Buffer Nowait %:	99.36	Redo NoWait %:	100.00
Buffer Hit %:	94.94	In-memory Sort %:	100.00
Library Hit %:	99.94	Soft Parse %:	99.91
Execute to Parse %:	31.66	Latch Hit %:	99.56
Parse CPU to Parse Elapsd %:	4.92	% Non-Parse CPU:	99.96

CPU time		4,924		40.6
db file sequential read	1,809,909	2,834	2	23.4	User I/O
gc cr multi block request