Within the installation disc, there should be a button which you can press to open up a list of tools you can use to repair your boot sector. If I remember correctly, The button should be located just before you install windows using the CD Key. Something about "Repair this computer". Within that, you should find numerous tools. One of which is, Automatic Repair/ Startup Repair. Try using it to see if it fixes the problem by itself. If not, Go open the built in command prompt (It should be there within the list as well) and type
bootrec /rebuildbcd
and then
bootrec /fixmbr
after that
bootrec /fixboot
Bootrec may scan your disk for recognizable operating systems during one of the operations. Since you only have one operating system, you can type in "Y" (Yes) to add it. This should fix the problem and get you back in to windows
Best of luck zack~