Store.Exe using 100% of CPU. Exch. 2000

I have a compaq PIII 1.o gig HZ with 1 gig Ram, W2K server with SPK2. This server is running Exchange 2000. I have rebooted this server many times. The problem is STORE.EXE uses 100% of CPU. When this happens no one came use Outlook and I have to reboot also the response time at the server console is too long. Does anyone have this problem and/or solution.
Many Thanks.