Hi,
During start up I got the message "Your disk drives are being checked for errors". But it went so fast that I could read following messages.
Once logged I though I could find it in "dmesg" but nothing...
May someone know where I can find plese ? 
This is probably nothing to worry about. The boot process will look at the filesystems to mount and check the status flag on each. If they are all marked as clean (i.e. unmounted correctly at shutdown) then the thing will whizz through. If there is a problem, it will either stop and prompt at the console or possibly try to fix simple problems, but you will at least see more output from this and it will take a little while usually.
It depends what flavour of OS you have as to what it does. Some versions stop and prompt for the root password so you can get into Single User and you manually fix things there.
On the whole, if it runs, it runs. Don't worry, it is a normal checking function.
thank you rbatte1 ... but I confess I'm not so quiet cause the word "error" is quite deep for me x)
"unfortunatly" I'm running under ubuntu which does a lot of things automatically ... as this OS is done for NOOB like me lol ^^
You can't claim to be a complete noob if you are using dmesg and interested in the the messages. Have confidence. Everyone has to learn and it looks like you want to.
I can't claim to be an authority on much, I'm just trying to find a way of paying back for help I've had in the past. Hopefully I won't suggest something outrageous.
Robin