I have a dotnet windows service that's currently hung, but running. Is there anyway to attach a debugger to it, despite the lack of symbols; and that it's already running?
Ignore the "no symbols" warning. Once you have a native debugger attached (i prefer WinDbg for stuff like this), then load up the SoS tool pack:
.loadby sos mscorwks
Now you can get a managed callstack using the !clrstack command, and hope that gives you enough information to figure out the hang. Here's a handy cheat-sheet with a few others if that doesn't do it for you.
Won't help you this time, but... get in the habit of turning on symbol file generation for debug and release-mode builds. There's no reason not to, and it'll make your life a bit easier in situations like this.