How can I tell if the qt client is actually staking my coins?
I'm pretty sure my coins are old enough (more than 8hrs) if you asked.
under Balance there is Stake: 0.00 CAPT
if this Stake has some numbers that means it's waiting to mature right?
Yes, stake is the amount waiting to mature.
After it matured, it will pass to balance again.
Why is my stake showing 0 CAPT and I had coins in my wallet for over a week now?
A 'Stake' of 0 only means that nothing is pending. Your stake is the part of your balance
that you can't spend yet because it has just staked.
It doesn't mean that your wallet hasn't ever staked (it doesn't mean it has either, though).
As Kebooz said: in 'Transactions', in the second column, you can filter to see only 'Mined'.
There you can check if you've staked. Have you?
If not: Is your wallet unlocked (or not encrypted at all) and has it been online?
If you haven't staked yet, just make sure your wallet is unlocked and online.
It depends on the luck.