or use similar tool like DBAN
http://dban.sourceforge.net/

Wiping it completely should help you recover the drive's size and there you can start to fresh install Windows.

If this incident started only when you plug-in the SD card, I suggest that before you use DBAN to wipe your computer... reformat the SD card because that is maybe infected when you tried to plugin and access it. Did you plug it in and access the SD card?