If a computer system placed in water for one hour, can we gain success by blowing air to all parts and computer gets started again?

of course you can start again your system. 
I can't guarantee it will work & operate like before No hair dyers or any forced air on/into a closed device! you'll only be spreading any liquid/water not drained around inside where you can't see or get at it.
"don't shake it to get water out" The electrolytic activity of combining electricity and liquids will begin as soon as the liquid contacts the powered circuits so if it was removed the power and battery you have to make sure that it is completely dry disassemble the computer, Forced air on the open parts With out completely dry water from the system circuits will be fired and you can’t back.
If data on your computer is important, you can remove the Hard Drive and read its information by connecting it to another computer, even if yours does not work any more.
I can't guarantee it will work & operate like before but at least all the spilled water are gone and they did not short out any of the electrical circuits or components...
Basically by opening it up and if you reassemble it, then say if it still didn't work at least the repair technician if this PC is still under warranty?

OF  COURSE IT WILL.
if computer system is laptop or Desktop, you should dismantle THE PARTS, remove each part of that system and dry it by itself.
except for the Hard Drive, everything will work correctly.
  the hard drive is a bit hard to dry, and maybe some water will get inside, so you should put it in a bag of rice for a day or something, and then try it again.

If placed in water while working then replace it.
If it was disconnected from power source, then you have to make sure that it is completely dry as to avoid having the circuits fried.
A proven way to completely dry any electrical device is to place in rice over night, i.e.
some hours, as rice will absorb all water in it.

Absolutely, provided the machine was off and you should not put on, blow it thoroughly if possible remove all components like Ram, hard disk, processor,powersupply and  Dvd rom.
blow them separately then connect again after ensuring its dry completely the machine should work.
However if its sality water corrosion takes place faster hence easily affecting some componets like Ram in this case you might need to replace them.

yes it is possible.
We got this experience after flood and all machines were operational after blowing air and cleaning.
Just don't turn on the computer.

i think yes>>>>>>>>>

Hard drive and DVD RW may stop working, while other parts can work if water is drained out properly 

yes

at least you have to let it dry then try to clean the parts one by one carefully.
then re-connects the parts and trun it on.

if we put it in water while it's running it will damage dirictly and if we puting it will it's switch of power i think we must open the computer and and uninstall all the part  processor rams hard disk dvd drive vga cards - ethernet card-etc from the motherboard and drying them by blowing warm air throgh of them but mabe some parts will damge by water like hard disk if the wter go inside also mabe the vans of the processor or the power supply will damage by water also the speaker of alams will damge and the coil of the mother board if the water go in side the mother board will damage also the same for the power supply and the another cards  for that i think the computer will not start again dirictly mabe we need to replace some parts and and try to start it again then the system will start again