In Excel, click the Office button (top left corner) then click Excel Options. Select 'Trust Center' and then click 'Trust Center Settings...' to the right of that. Click 'Macro Settings' and make sure it's set to 'Disable all macros with notification'. Click OK twice to return to Excel.
Whenever you open that XLSM file in the future, you should see a prompt below the toolbar (above the cells) notifying you that macros need to be enabled. If you disregard that notification, macros won't run for that Excel session.
Your other option is to save the file in XLS (Excel 97-2003) format. You should get the same prompt, though. You can't save a workbook with macro (VBA) code as XLSX (the standard for Excel 2007/2010).
Back in the Trust Center Settings, you can add Trusted Locations either on your PC or on the network, which will stop Excel from notifying you about macros and simply enable them when you open files stored in those locations.
If that's all well and good, perhaps you ran a macro that disabled your events. To fix that, open a blank workbook and press ALT+F11 to open the VB Editor window. Paste the following code into that window and run it. Close that workbook without saving, and then try to open your faulty workbook and run the macro again.