Cannot load Farmville on Facebook.

i guess ur using a licensed and updated antivirus (i prefer avg/kaspersky)..!!
this is a common problem now days, probably itz caused by a virus/trojan..

try using only --
http://login.facebook.com/login.php

download microsoft KB890830, install n run

also possibilities of:
u may not hv java runtime/adobe flash player/shockwave player installed..
the windows firewall is limiting the site..
may b ur antivirus is doing so..
some spyware/trojan horse also may play foul..
sometime it also depends upon the browser u r using..
may b it is black-listed or restricted by using 'content advisor' (in case of ie) in ur computer by some user or the above..
may b it is being filtered by the 'phishing filter'..
there may b possibilities that the site may contain 'active content'....