hdparm - w /dev/sr0
(this will try reseting/unsticking your cdrom but beware
hdparm -w : Perform a device reset (DANGEROUS). Do NOT use this option. It exists for unlikely situations where a reboot might otherwise be required to get a confused drive back into a useable state.)
then try remounting it
does your cdrom work fine under windows?
if it works fine under windows, then try turning the cdrom's dma off in linux with
hdparm -d0 /dev/sr0
if you have the same problem under both windows and linux, then it's clearly a hardware problem.
i have the same problem with my dvd, clearly a hardware problem. until i buy a new one, i take out it's power supply and remount every time that it hangs, but i wouldn't suggest it to anyone)