I have installed `Ubuntu 12.04` on my laptop.Every thing is working fine.But from last two days I am facing a problem and that is when I am going to `shutdown my system`,it is showing the `shutdown process` but it is actually `not doing shut down`.`The screen is reaming like that for many time` then I am doing the `forcibly shutdown by pressing the start key of my system`.Can someone tell me what is the wrong going on?Any help and suggestions will be highly appreciable.

**[update]**

When the shutdown process was going on I just pressed the `esc` key and it showed the `error message` like this

```
modem manager[878]:<info>Caught signal 15,is shutting down...        [Fail]

```