Hi Yeehat and thanks for your replay.
Doing my MacBook Pro is a production machine i preferred to not waste more time to proof understand the issue and try to solve it by a workaround.
So i have reinstalled SL and it's last combo update, repaired system permission by installation disk. Now all works fine and have had no problem with applications and other settings. Magic: no loss of data or app settings. Now Office file quick look previews all files (old and new).
Font Library also works well, except about a font that which it's probably corrupted (or not compatible even if it seems to be)
At the moment i've not installed the last security update...I'm too afraid of having to start all over again :-)))
First I'll try to read up best on solutions in case Quick Look do still the same issue.
I know that it is not a "solution" but i was wasting too much job time. I think i will survive a few more weeks without it !!! :-)
Thanks again