Well, if you have root access to your server (asuming it is *nix type) you can run this benchmark test program:[qcode]ab -kc 20 -t 30 http://yoursiteaddress/[/qcode]
20 - number of simultenious connections.
30 - seconds the test will continue
When its done, it should show you what went wrong (if anything) and how much time it spent on requests, etc.
For best results it should be done from another server, so it could also test the network.