I have a lot of idle processing power, some of them even with free electric supply, but they all have poor network access (may of them even have no network access)  so I cant rent them out as a VPS or something like webserver ……

I found bitcoin mining maybe a good way to make use of them, but I am not sure whether it's the best way.
Is there anyother way I can sell/rent the processing power?

BTW:
Most of them are server boxes, they have powerful CPU and pool GPU (I am not sure it could call GPU or not just a onboard video chip)
They are good at float computing not SHA-256......

Thanks,
CreateFile

Yes, It's the problem, CPUs are good at float computing, not doing SHA-256……
Is there any way to sell cpu float processing power?

You might be able to sell FLOPS for Bitcoin.

You could set up a seperate server that specifies problem format and accepts Bitcoins and the problem.  Sneakernet it over to your CPU.
Bit of a hassle, though.