Fortunately for me, it's now solved .
All this was the fault of Java. Looks like the upgrade to SE 7 U71 went wrong. I restored Win 7 before the Java upgrade... but previous SE 7 U67 was also broken . I managed to install U71 and this time it worked, fortunately !
Now everything looks like working fine.
So to answer my own question Could an issue with Java give FM headaches ? the answer is YES !!!