OS 10.5 - Problem on MAC OS, kernel_task process

Hi

I always used to make some audio chat over iChat. But on last saturday, when i received the invite to an audio chat, my computer stopped, and the only way to interact with him was when i turn off in the power button. From this last saturday, my computer never more restarted, he stay with the busy icon and do not make anything.

Today, i see in the activity monitor, that there is a process called kernel-task that in only 5 minutes, generate more than 1700 threads. My computer don't turn off if i ask, just if i press on power button.

There is something that i can do to have my system working again???

Thank you for your help. At this moment, there is more than 1500 threads. My computer is very slow...