[Newbies] Debugging Squeak

Hi, I was trying to make some modifications on Squeak. After some coding work,I found my Squeak now consumes almost 95% CPU time and more than 100M mem, and it seems like it won't slow down unless i close it. I've already saved the image and the CPU consuming problem comes out right after starting Squeak with out running any code I wrote, my question is, is there any debugging tools that i could find out which process or chunk of code is slowing down my squeak ? I've tried MessageTally,didn't work.

Thanks~

K.Chang