A QuickBooks Company file may not open for a number of reasons. It may have become damaged the last time it was in use, or it may have been damaged due to some form of corruption on your hard drive where the file is stored. Other common factors include problems with reports or transaction templates that were left open within the file the last time it was closed (especially if you have the preference selected to ‘save desktop upon exit’. Other reasons include using the wrong version of QuickBooks, or issues with the location of the file such as access permissions, problems with the file name and file extension, or a conflicting *QBW.tlg file are additional reasons why you might not be able to open the file.
You may experience various error messages including the -6000 series (there are several), or the H### series, C= errors (such as C=343 or C=422, although these are rare), various Unrecoverable Errors (I wrote an article about this last week) and many more.
Preliminary Step: ....