Can you view the file here, using Autodesk's online file viewer? If not, then it's probably corrupt.
• Go into the same folder as the DWG file, and look for the same named file, but with a .BAK file extension (You need to have file extension TURNED ON).
• This is the last save before your last save.
• Then rename that file from BAK to DWG and try that one.
• If that doesn't work, then go into your %temp% folder (in the address bar of Windows Explorer, type in %TEMP% and press enter).
• Sort by date and look for a file name similar to your original file, but with a .SV$ file extension.
• Rename that to .DWG and try it.
• This is your last Autosave file (it may not exist)
• If that does not work, look for the same named file in the %TEMP% folder with a .BAK file extension.
• This will be your next to last autosave file. It may not exist either.
• If it does, rename it to repair autocad file and try to open it.