Problems with SnagIt could be due to the inability for your computer to reach the web via FTP. This ability may be easily tested from a Command (DOS) prompt.
You'll find the Command prompt program under Accessories:
Once at the command prompt, give the command:
ftp
ftp.iris.washington.edu
For User, type: ftp
For Password, give your full E-mail address:
soANDso@foo.com
If ftp is working, then the response will be as in the image below:
If not, then the computer technicians at your school will need to help out.