SMTP SENDING OUT SPAM

I HAVE BEEN INFORMED BY MY ISP THAT MY SMTP IS SENDING OUT SPAM. MY ISP HAS SHUT DOWN THAT SMTP SO THAT I CANNOT SEND OUT EMAIL UNTIL WE FIND THE PROBLEM. I HAVE DONE A SCAN AND FOUND A COUPLE OF WIN32 PROBLEMS AND HAVE TAKEN CARE OF THOSE, BUT I STILL HAVE THE PROBLEM. I NEED HELP ON THIS ONE. ANY SUGGESTIONS WILL BE GREATLY APPRECIATED. IS THERE ANOTHER PROGRAM THAT CAN SCAN AND FIND THE PROBLEM. I TRIED TREND HOUSECALL BUT IT WILL NOT DOWNLOAD AND SCAN PROPERLY.