So basically if there is somekind of formula to change the the decimal of the date to date it would also help.
what do you mean? Are you importing data that is dd.mm.yyyy? or pasting?
My suggestion would be to import or paste this into cells formatted as TEXT. Then use this formula to covert it into a date value (in any cell not formatted as text):
(assuming the date that was pasted as text is in column B starting in row 2):
=DATE(RIGHT(B2,4),MID(B2,FIND(".",B2)+1,FIND(".",B2,FIND(".",B2)+1)-FIND(".",B2)-1),LEFT(B2,FIND(".",B2)-1))
To see it more clearly:
=DATE(RIGHT(B2,4),
MID(B2,FIND("/",B2)+1,FIND("/",B2,FIND("/",B2)+1)-FIND("/",B2)-1),
LEFT(B2,FIND("/",B2)-1))