Deposits to an Offline Wallet
Bitcoins are stored in a decentralized ledger called the blockchain.  When your computer is shutdown the blockchain stores the balance in your associated public key also known as an address.  If you are using the reference client (Bitcoin-qt) you will be able to spend your Bitcoins once the computer is turned back on and the blockchain has downloaded all of the transactions that have occurred since it was turned off.   So while your PC is off yes you can still receive Bitcoins because the rest of the network has seen the transaction that is incoming to your address and they will continue to store that information indefinitely.