Often this is because ConQuest's configuration files have become corrupted and deleting them solves the problem.
Go to your home directory (type %USERPROFILE% into the Windows Explorer bar) then go to the View tab and make sure "File name extensions" and "Hidden items" are ticked. Delete the csds_data folder and any .csds_defaults or .csds_defaults[number] files, then try to run ConQuest again.
Another cause of this problem is having an old version of ChemOffice installed. ChemOffice puts its old version of opengl32.dll in the system PATH and ConQuest tries to use this library and gets confused because it is too old. Rename the folder "C:\Program Files (x86)\ChemOffice2002" and try running ConQuest again.
A complete reinstall of the CSD software may also resolve the issue.