Excel runs really slow after macros. help!!

Hi all,

I'm new to excel and I'm having a problem with the macros I've made. Basically, I'm running through a big loop about 500 times over during the macro. The first time I ran it it worked pretty well, but the more times i use it the slower excel becomes. Now my workbook runs incredibly slow even when i'm not running the macro anymore. Exiting and restarting my file doesnt seem to fix anything either. Can anyone give me any advice about why this is happening? Thanks so much!

I am using excel 2007 if that makes any difference

Show us the code and tell us what it does (in business terms).