Typically, "hangs" occur most often when using X from the console. That's because kernel messages (such as a kernel panic), and dropping into the ddb(4) debugger, are hidden from you.
If you have a "hang" while using X, you can determine if the computer is still running only by access from the network. This requires a network and a second computer. You can see if the box responds to a ping, and if you can connect to a service such as sshd (if the service was configured to run).
The only way to "see" what's on the console (such as a panic followed by ddb) when using X is to connect a serial console. I have one, it's an old Palm PDA, with it's old 9-pin serial connector and some freeware/shareware PDA software that emulates a VT100 terminal.
If whatever is happening allows the OS to keep running, you can look at /var/log/messages and /var/log/daemon for possible messages.
If you're not using X, you usually won't see "hangs" unless there is some sort of hardware problem. Let's find out what your actual symptoms are, first.
