Anyway OP, if you're still interested in mining with your computer then you could try mining altcoins and converting these to bitcoins using an altcoin exchange like Cryptsy. There are many altcoins out there which can still be mined using CPUs or GPUs. The only ones which have ASICs built for them are SHA-256 based coins like Bitcoin and Peercoin, and scrypt-based coins like Litecoin and Dogecoin.
Agree. In most country, the electricity cost will never make you profit mining Bitcoin. However, mining altcoin might give you a little profit. Well, most altcoin difficulty is lower compared to Bitcoin. Also, instead of mining by yourself, joining a pool might speed it up. If you intend to mine Altcoin and join a pool.. Choose a pool which will automatically mine profitable altcoin and exchange it into Bitcoin for you.
It's not because of electricity costs that mining Bitcoin using general purpose hardware is a bad idea. It's because of ASICs. A single ASIC is equivalent to an entire warehouse full of computers. If a coin has ASICs developed for it, then these ASICs are competing with your single computer for the same block reward and because of this, your single computer always inevitably loses. Even tiny SHA-256 coins like Betacoin and Terracoin can't really be mined using CPUs or GPUs anymore in any reasonable sense because the existence of a single ASIC mining on the network is enough to outclass hundreds of CPU and GPU miners.
Actually it is indeed about the cost of electricity. The presence of ASICs drives up the difficulty, but at the end of the day it comes down to the cost of producing X units of a coin. An ASIC, as you correctly point out is considerably more efficient at hashing than a CPU, GPU or FPGA. The most efficient ASICs out right now are hashing at between 0.4 and 0.5 Watts per GH/s. Even more efficient gear is on the horizon (and likely already being tested/mined).
Sure, back 3 and 4 years ago mining Bitcoin with a CPU was indeed a viable option. Then people figured out that using a GPU was more efficient - you got more bang for your electricity dollar. Then along came FPGA, which were even better. Finally came the ASICs, which are even better still.
Why would you use your 450W Radeon R9 295X to mine BTC, getting speeds measured in MH/s, when you could spend that same 450W on two ancient overclocked S1s getting 400GH/s (or newer gear for greater hash speed and less power draw)? It's all about the cost of that precious fuel (i.e. electricity) powering your devices. Right now, with the exchange rate of BTC, even relatively new gear struggles to earn you anything above and beyond the cost of operating it. For example, assuming you've got power costs of $0.10 per kWh, an S5 would only expect to bring in $1.47 a day. An S3 would only expect to make $0.29 a day.
As you can see, it isn't even worth thinking about firing up that CPU/GPU to mine BTC because all you're going to do is burn electricity for no reward.
