my Meriam Instruments MeriCal DP200I is locked up HELP!!

[USMCPMEL]

Ok so I went to zero my Merical yesterday and ...... It was not so merry!!! It locked up on me. I left it on overnight in the hopes that the batteries would drain and it could be restarted. No luck so far and I need to use it today. Is there some magical key code combination I can use to get it unlocked?