If the workbook is, in fact opening, there are two possible solutions:
If the workbook is minimized or moved off screen then, after opening the workbook, press CTRL+F10 to maximize the window.
If pressing CTRL+F10 does not work, choose the menu command Window->Unhide (On Excel 2007 press ALT, W, U) to open the Unhide dialog, select the workbook to unhide if found, and click OK.
Kevin