Formulas no longer working

All of a sudden all my formulas stopped working. My macros are functioning but thats it. A simple one like =F13 doesn't work. I have a copy of the file on my laptop which works great. If I clear all formatting for the 2 cells it will work the first time only. I am confused and disappointed. Any suggestions? Its excel on a work server so a reinstall is out.

EDIT: I have tried checked the automatic tick under the calculations tab as mentioned in other posts. I have also tried to format both as general. WHen I change the value in one cell such as B1 it will not put the same value into A1 if A1 contains =B1
It will however change once I close and reopen. I cannot keep doing that to make it work. HELP!!!!!

If you mean that the calculated values are not updating when the referenced data changes....try this

Press the [F9] key....to force the workbook to recalculate.
If the correct values display, then you have Calculation set to: Manual

From the Excel Main Menu:
<tools><options><calculation tab>
AUTOMATIC should be checked

Does that help?