The command line prompt is simply PING.
For example, "ping discusscooking.com".
I agree with Frank that pinging a server isn't a very good test. All it really tells you is that there is a server there.
I'm also glad he mentioned that DC uses a CDN, or Content Delivery Network. That can play a big factor in how fast or slow a site is. CDNs essentially duplicate a web site's content (images, etc.) in various locations around the globe. In theory, you are supposed to be fed content by the server closest to your location. Perhaps the one closest to Andy is having some problems. This might also help explain why he was seeing images with red x's, while others were not having any issues.
I work in the IT department of the world's largest real estate network, and we use a CDN to distribute web traffic to our websites. We have millions of visitors to our websites every day, and having the images and what not available in dozens of servers around the world keeps traffic from all going to one single location, which would make things unbearably slow for anyone browsing our sites. The down side is that it sometimes takes a while to replicate the content everywhere, so it can occasionally appear that images are missing.