Amazon blocked by firewall?

Amazon.com is unusable on my desktop, regardless of which internet browser I use. Almost all access attempts time out.  I can access it normally from other computers on my home network so it doesn't seem to be a network or router problem. Other sites load just fine from my desktop. Could this be a firewall problem?  If so, what do I do about it? If not, any ideas on troubleshooting?

Thanks!