Oh I see you have a large HDD (750GB) and you partitioned it yes?
It sounds very much like the main windows partition has been removed. If Windows is
If you have a Windows 8 install disk then I'd change the boot order and boot off that. I guess the only issue would be if your copy of windows was held in a partition and that was removed too?
Re-install Windows 8.
You can take care of any partitions during the install process or once you've installed use the storage manager via admin tools.