Can't download anti virus updates

Hello,
I have a problem. My AVG anti virus has notified me that my laptop is infected with a virus -- a trojan to be exact. The problem is it can't be healed. To make matters worse, I can no longer download anti virus updates or even do an online virus scan! There is always a notification that says link appears to be broken. Please help! ASAP. What will I do? Thanks a lot!