you didn't mention when Weblogic hangs, Does send an error or not .
If it sends a "Memory out of usage " error plz send me an email then i tell you do something to fix it .
Making just one connection pool for one db is enough and there is no need to make 5 pools.
how many connections have set for ur pool?

Nor weblogic  console nither myserver.log doesn't show
any problem!

Our "Memory out of usage" error is solved by
increasing heap size.
I test on connection, but this problem  is stil
consist.
I use hibernate  for data layer.it make connections for
users (about 200 user)

There is a figure in connection Tab that shows the rate of memory usage and cpu and some other usefull reports.
By the way , with this condition that there is no note from weblogic  and i have no overall vision on problem.
I can only give some global comments:
1- since u use hibernate  , there may be some problem  with hibernate session factory bcuz it is so weak and can not afford under high load.
2- ur pooling method for connections in weblogic is not well .
3- changing weblogic JVM to JRockIt may be a nice try.
4-there may be problem in oracle  with oracle query caching.here i put a question.how is repsonse speed of ur appliation?
5-I dont know about carcked version of weblogic with 5 users  license;the version that we use has no limit for users. may be this is the reason of ur prob.-i have a web  application with the same spec but with nearly 3 times more users and it works.-

I will have to disagree with the first point since hibernate  delivers a fantabulastic performance even under load. I have also never noticed any significant performance difference with JRockit. In theory it handles memory issues a lot better, but my experiences were not very impressing. One thing that is worth looking into is to check how many http threads the web  container has. You may have to increase the number so that you can accept more concurrent users; however, this should be used after you are sure your hardware capacity is not maxed out. In addition having 5 connection pools is rather strange unless you have a good reason for it. You may also want to check if the connection pools are maxed out. A better description of how dead WLS is will also be a help in finding the problem.

I have to explain about my experiences about this matter:
1- I do agree that the problem  may be because of number Threads.in the previous mail I forgot to mention that the number of idle threads should be checked.
2- I can prove that the Session Factory of Hibernate is so weak under high load.the mechanism of pooling of session can not perform well when the requests get high and should be used some extra jar files such as C3P0.
3- It is very simple to distinguish the difference of JDK and JRockIt performance.In equal condition ,just change JVM of Weblogic and check the Figure of memory usage in connection tab.

Some times WLS show this error in myserver log:
Could not execute JDBC batch update
And after that nothing work!!
My other question is why, when users  want to login (I
thing when hibernate.cfg wants to create its
connection and it's ...) it makes several Seconds!!
(About 10 Sec.). Is it naturally or not? (When I used
EJB 2.0 or DAO there wasn’t this delay!)
About MR Arghand’s comments:
So thanks for your attentions and reply,
1-How can I change my pooling method for connections?
2-i checked oracle  query caching and response speed of
my application,I don’t think that there is a problem.
3- Can we have your version of Weblogic?
4-i change WLS JVM to JRockIt, but my problem  still
exists!