I am experiencing strangely disappearing windows. It first occurred when I was working on a spreadsheet in Excel. The sheet was behind another app but when i went to look for it, it was gone. It was still on the dropdown list under window but if I clicked on it, nothing. I could not reopen again either. My solution was to close Excel, reopen the file in OpenOffice and save it with a new name. I was then able to open the sheet normally in Excel. Now I have invisible windows in Apple Mail. Normally I open Mail on startup and leave it running in the dock. If I click on the dock icon, I expect a window with my inbox to appear. Now nothing appears. Sometimes I can get an inbox by using the menu File>New Viewer Window but sometimes I have to close and reopen the app for it to work. If I go to the Window dropdown, the app says that I have seven versions of my Inbox window (one with a diamond and one with a check mark). I have a nightly automatic backup (CarbonCopyCloner) but think that is no use since the problem is several days old. I also have a monthly backup that predates the problem but I am afraid to restore from it if I might lose recent emails that I have moved to folders on my computer. Any ideas will be appreciated.