I've spent hours trying to resolve this issue. Reinstalling did not fix it either.
 
One of my project files does not play the metronome at all. I've tried creating new projects and it works fine there. It has worked previously.
 
 

 
 
I normally do not want a metronome in my projects.
 
Instead, I generally import a drum track or use my drum synth to create one. To me, it's just more natural to play to a drummer than to keep time with a midi click.
 
The metronome controls are immediately to the right of the BLUE box with the time display. The 3 stacked boxes with the metronome icon and the 2 above it control what you hear, and when you hear it.
 
Have you enabled it in the tool bar to give you sound?  
 

Fair question, guitarhacker.
 
I am a big fan of using the metronome & a drum track at the same time.
 
As for your question, yes. I've enabled the metronome for playback and recording. I've verified that the output is set to the hardware that I'm using. I've verified the the sound files exist (found the location in the project file via opening it in notepad). I've used the metronome successfully in new projects AND I've used the metronome in this project previously. 
 
So I'm looking in to a way to move all my data into a fresh project. Frustrating and in my opinion far from necessary.
 
WIsh me luck.

update & double post.
 
solution found!
 
upon saving my project as a new project (opening project with issue > FIle> save as...) it's all fine.
 
It's probably an issue with the project file itself but I don't develop the software so I can only guess.
 
Thanks for reading and I hope this helps

never mind. same problem happening again. 
 
retried old solution. no luck.
 
this is starting to get old and frustrating. I really shouldn't have to spend this much time trying to solve this issue.

OK.. I have had some issues with project sound.... and copying to a new project...track by track did work.
 
So.. if the issue is at first resolved by copying to a new project but them sound goes away...... what are you doing in between the copy and the sound going away?
 
Also..... what computer, OS, sound card and driver are you using ?

Thanks for your reply GuitarHacker. In the meantime I have done what you suggested and simply created my own click track. At least it works consistently; it just creates more work.
 
OS: Windows 7
Sound Card(s): Line 6 GX, Steinberg CI2 (not run together, but used for different purposes)
Driver: ASIO
 
As for what I'm doing in between the copy and the sound going away I'm simply recording guitars & bass  through the GX and vocals through the CI2. I can't exactly pinpoint when the program decides to stop using the metronome but I have a feeling it's during the switching of devices. A big reason why I think that that is the case is simply because I cannot change the sound levels of the beats in the project that has the metronome issue; they simply revert to whatever was remembered last.
 
Having said that, even though it would be easier (in general) to use the in built metronome I've given up with it. I'm over trying to find a fix for this issue as it's taken up enough hours where I could have done something more constructive.
 
Thanks for your help.

You can easily save a midi loop somewhere convenient and just drag it in to a new project, assign the drum synth and waa laa....  it only takes a minute literally, to create the drum/timing track.
 
Use a decent sounding drum synth and you will like it even better.  Generally, at some point in the song creation process, you are going to put a drum track in it anyway.....so why not start with the drum track.... or at least a basic track that can then later be modified and edited as needed.
 
Even if I'm recording something that will have no drums, such as a straight up piano or acoustic guitar vocal sort of thing..... I use a drum track for the timing track.....it's just so much easier to hear the drums vs a click. Once I get the instrument track in place and on time, I mute the drums.
 
I used to use Jamstix almost exclusively as my drum synth. I simply placed one midi note in measure 130 and told Jamstix to jam to the midi. It would start in the count in and play all the way to that measure (130) and stop. Most songs are way less then 130 measures so once the songs actual length was established, I would go back and edit JS to end in the proper place.  I would then drop in the fills and such things.....I would spend an hour or so editing the drum track as I worked. Considering that many songs would have dozens of hours of work in them, an hour or two on the drum track was not much.

Guitarhacker
You can easily save a midi loop somewhere convenient and just drag it in to a new project, assign the drum synth and waa laa....  it only takes a minute literally, to create the drum/timing track.
 
Use a decent sounding drum synth and you will like it even better.  Generally, at some point in the song creation process, you are going to put a drum track in it anyway.....so why not start with the drum track.... or at least a basic track that can then later be modified and edited as needed.

 
I realise that it doesn't take that long to create a click track using a drum synth. That's what I'm doing now. The reason that I want to use the metronome is because I can use a 4 count intro into whatever track I wish to record on.
 
In order for me to correct mistakes in a certain track I now need to
1) create a new track.
2) record what I want on this new track
3) put it into the old track (as I find it neater)
 
instead of
1) place my cursor where I want on the current track.
2) record what I want, where I want it.
 
The whole process is simplified in both cases but it is basically extra (unnecessary) steps to achieve the same thing by not using the metronome.
 
I am using EZdrummer for my drums but that's beside the point. I like having a click track while I record.
 
It's also quicker to configure the metronome instead of synth drums to get a sound that cuts through the mix more easily.
 
In other words the solution you provided (and the one that I'm using) is great but it's a workaround that requires more steps and that is simply something that I find annoying because a feature exists in the program to do what I want but it doesn't work properly.

Each time you change recording devices, are you changing what device the metronome plays through?
Have you tried punch recording to correct mistakes? This allows you to play along to your recorded tracks but will only record what you're playing at the places you selected.