What computer operating system? What was your last activity in the project just before you saved closed it? Are any of the AutoSaves usable?
Please do the following
a. Please make a copy of the project file, rename the copy and try to open the copied project.
b. After you saved, closed the project, did you move, delete, or rename file and folders that went into the project?
c. Is this a "it worked before but not now" or "it never worked before problem"?
d. Is the problem just for this one project or all that you create and save close and try to reopen?
e. Did you install Premiere Elements 14 to the default Local Disk C location?
Please consider, and then we can decide what next based on the details in your reply.
Problems with the same symptoms can (often do) have different causes. In that context, please check out sampling of reports for Premiere Elements and your specific error message