EXchange2000 Issue

Store.exe and CPU 100% Usage
Recently, my email Ex2K enterprise server always shows us up the store.exe and CPU 100% usage and all clients are unable to access, we could not stop / restart the service and have to reboot the server for recovery, but then over a period time of about serveral hours, it occurs again. very painful!!!!
We have found serveral articles on techpublic and MS knowledges Base and it really exist such kind of solution by loading the patch and Sp2 or 3. but after we upgrade patches and SP2, and then SP3, there is no any improvement, still remains the same.
Experts, please help me to figure it out....!!!
I am the IT manager and serve a volumn of users as 400 - 500. and we are planning to replace the server, but needs to waiting the complex approval and vendor delivery and so....

Thanks in advance.

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