Blacklisted ??

What is this message that keeps popping up when I try and log onto my blog?

Your Internet Protocol address is listed on a blacklist of addresses involved in malicious or illegal activity.

I use this site for my classroom and I have certainly not been involved in malicious or illegal activity. I have recieved about four strange e-mails with the subject Trackback. They appear to be from strange companies?

I am quite concerned about this and the fact that I am locked out of my blog for who knows what. My students and parents depend on this site. Please let me know how to correct this problem immediately.

Thanks