Windows 7 "no bootable disks found"

Dear Apple Community,

My iMac (Mid 2010)(with cd-drive)could not boot into the windows partition. What I do normally is that I press the alt key while I turn on my imac, and then boot into windows 7. However, today when I press the alt key, only the Macintosh hd partition is bootable, with no option for windows 7. When I tried to boot into windows 7 using startup disk in preferences, the computer boots into a black screen with "No bootable device, insert disk and press any key". How can I boot into my windows partition again? This issues started when I created a new partition from the left over partition of Macintosh hd without any changes to my windows partition i.e. I have a 500 hdd previously I had created 250 gb partition for windows and Mac OS each but after creating a partition of 50gb I got stuck on the above mentioned problem I reverted the partition back to it's original 250 gb partition but nothing changed. Plzz help asap.

Thank you!!!