Return oldest date in range when a file is open

Hi,

I'm setting up a spreadsheet to keep track of case files within our office.
I'm having trouble with one formula. I want it to display the "Oldest open file." In other words, to return the oldest date in a column ("Date all docs received"), but to ignore closed files (where a date is present in the "file closed" column).

I have tried to array enter this:

=MIN(IF(Michael!K2:K999=0, Michael!C2:C999))

Which returns "1900-01-00". My theory is that the formula is treating all the blank cells as zero, which reverts to 1900-01-00 when formatted as a date.

How can I get the formula to ignore the blank cells from the MIN calculation?
OR, is there a better formula to use?

Thank you.Mediation Tracking Feb-05-2016.xlsx

Try

=MIN(IF((Michael!J2:J999=0)*(Michael!C2:C999>0),Michael!C2:C999))

Enter with Ctrl+Shift+enter

The "*" is an AND condition in this formula

JohnTopley's answer did the trick, thank you.

Thanks ChemistB but that formula would not exclude closed files.