Some people have come across an issue where they suddenly find a inaccessible Q: drive appear in My Computer in Windows 7. However I have found that this isn't Windows but Microsoft Office.
If you use Office 2010 Starter Edition or similar lite versions of Microsoft Office products, you will find a new Q: drive setup on you computer.
This Q: drive is setup by Microsoft Office for Click-to-Start type applications. This can be thought of a virtual drive that can only be used by Microsoft Office. This is a allocation where the applications can be downloaded and run from. Click-to-Start applications aren't fully install and are downloaded partially each time you run the application.
The Q: cannot be access in any form. The new Q: drive is need for Microsoft Office 2010 Starter Edition. You cannot hide or remove this Q: drive.
For more information, see here.