Hi

This was working well a while ago
I have a collective entry form at the front of my website
That used to be working. but now everytime someone submit an entry,
it will go automatically go to 31 dec 1969!!!?

Is pmachine hacked?

That date is what PHP returns if you have a date in an invalid format.  The date format that pM Pro uses can only store dates from Jan 1, 1970 and forward; anything before that (or in a bad format) is displayed as Dec 31, 1969.  If entries made with a collective entry form are getting the wrong date, then the most likely reason would be that the date field in your database got corrupted or something is wrong with your files.

Did you make any changes to the site/configuration (or did your Host do anything to the server) between when it was working and when it stopped?

Is there any way to allow dates before 1970?  I have a client who needs to enter many dates in the 1960’s and I’m hoping that this is still possible with EE.