Having trouble keeping entering time on a time sheet

Hi,

I have a timesheet that I enter time in on a daily basis. The time sheet calculates my time for the day. The problem I am having is that when I enter time such as 12:00, the worksheet automatically selects Am. If I enter 12:00 AM and I enter another time such as 9:00, it will make that time 9:00 AM. I want to know how to keep the time following in the correct pattern, ie if i enter 12:00 PM , then enter 1:00 in the next cell it will make the time 1:00 PM not 1:00 AM. Any help is appreciated.

Thank You,
Cranetech