I installed RHEL 5.1 on a Dell PE2950 server, but after I registered with Red Hat Network and Updated the system, the system became very slowly, I used free and top command to check the memory and cpu, it seemed ok. Then I booted from runlevel 3, it run normally, I tried to start X server, it became slowly again and it took me more than 10 minutes to login GUI interface. And I tried the old kernel, which run well before the update, it also became slowly. I also tried to use the old X server configuration file, or re-configure the X server, nothing was working for me. Anybody know what's wrong with this case, I appreciate any advises or hints. Thanks in advance!

I take it you have a subscription with RedHat, so why don't you call them?