1. First - establish witch CPU (if you use multiple for redundancy) is active and is having a 100% load - you can do so by looking at the LED indicators on the front of the switch. The "Master" LED on the fabric that is currently active will be blinking, and the "CPU" LEDs will be lit up to match the corresponding utilization percentage. Both are located on the right side of the CPU card:
2. Now check if the CPU is not locked up - to do that, connect to the console port located on the left side of the CPU module, using the console cable that came with your device. Use the HyperTerminal with COM1-9600-8-None-1-None settings (you will need a laptop with a DB9 port or a USB-to-DB9 converter of course). Once connected and logged in, enter "show sys perf" to check CPU utilization - if the system is not locked up, you should see the value corresponding to the front-panel LEDs discussed above - proceed to troubleshooting (if it is locked up, well - reboot it, fail it over or call 1-800-4NORTEL).
3. Now, if you are able to run console commands on it - run the trace level on the CPU to determine what is causing such high load. To do that, in the command line execute:
trace screen off
trace level 8 3
(... wait for 10 seconds ...)
trace info tail
You should now be able to page through the raw text trace of the current CPU activity on your device - look for identifying values, such as IP addresses, switch interface (port) numbers, trunk id's... that should give you a clue where to start off troubleshooting the issue. Good luck!