That's a physical support for the weight of a monitor sitting on top of the case. It screws into a hole in the inside of the bottom case, courtesy of a trapped screw in the bottom of the tube. Unfortunately, and as appears to be the situation here, they often break.
You can either glue it back on to the bottom piece with the trapped screw, which is probably still screwed into position (unscrew, glue, replace) or pull it and toss it. Just refrain from putting anything really heavy on it without one (LCD monitor yes, 21" CRT no
). You could also possibly, and space allowing, slide another piece of tube over it and glue it in place to reinforce the join. The join doesn't have to be super-strong, just enough to keep the pieces aligned so the force is directed straight down through them.I'd also recommend vacuuming or blowing the dust out of there, particularly the power supply. You can dismantle it safely - while it's off
The 610, 660AV and 6100 share a design flaw where the dust mesh in the PS is on the wrong side of the airflow, and actually traps dust *in* the machine. So, if you do get in there, pull the filter and toss it. The air *in*take is under the hard drive bay at the front left; if it bothers you, you could add a filter there. I hear dryer sheets work well.Yes.