Are you seeing any orphaned blocks, or just nothing at all?

Edit: some very rough calculations:

Every minute, you should have a (your weight)/(network weight) chance of staking.

100/500e3

That's a 1 - 100/500e3 chance of not staking in any given minute.

That's a (1 - 100/500e3) ^ (24*60) = 0.75 chance of not staking in any given day

And a (1 - 100/500e3) ^ (24*60*23) = 0.00133 chance of not staking in 23 days

That's a 1 in 753 chance of not staking in 23 days.

So I'm saying there's a chance, but it seems likely by now that something's not working right.

Version v1.4.8 of the client, which I tagged for building yesterday and should have binaries available for download soon logs how long each staking attempt took, like this:

2015-02-18 05:09:45 stake took 7s
2015-02-18 05:10:00 stake took 6s
2015-02-18 05:10:17 stake took 7s
2015-02-18 05:10:32 stake took 6s
2015-02-18 05:10:49 stake took 7s
2015-02-18 05:11:03 successful stake took 5s
2015-02-18 05:11:03 CheckStake() : new proof-of-stake block found 

You can expect to see each attempt take 0s if you only have a small number of outputs to check each 16 seconds, but the fact that you see it at all is proof that it is attempting to stake.

Another thing to check is whether you have the client configured to hold your balance in "reserve". There's a setting where you can specify that you want to always keep a certain balance available, and that balance never attempts to stake. If you have it set to the same as your full balance you would see what you're seeing.