memory allocation and link navigation shutting down Enterprise manager

Hi everyone

can anyone suggest me how to resolve below 2 issues

Issue 1
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how to allocate upgraded memory space(24 GB) between Oracle and OS

We are using 32 bit windows 2003 XP server. Currently we have 4GB RAM.We introduced 20GB more RAM to system. But still CPU is utilising 4 GB only.Also we have done an experience as follows.

(1)Edited boot.ini file with /PAE

(2)Added a new registry under HKLM\Software\Oracle|Homex with type as RN_Z and value 1.2gb

(3)IN Oracle we changed the parameter value for USE_INIT_DATA_BUFFERS from FALSE to TRUE.

But this severely affected our Database.After changing that parameter, Database went down.Then we restarted using pfile.we created a new spfile from that pfile.

Issue 2
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2)Second issues is that when ever I navigate different links through Database Enterprise Manager (to check performance and other activities)DB is shutting down.This started happening recently after doing all the above workouts.

Please guide me to solve the above 2 issues

please let me know if u need the pfile and spfile content