DOSBox is a program that emulates an old PC running the Microsoft DOS operating system. Generally software designed for Microsoft Windows will not work under DOS or DOSBox. If you want Turbo C working on DOSBox you need an early edition that supports DOS rather than Windows, as they are different pieces of software.
If you just want to get Turbo C to work on your 64-bit Windows 7 system you may want to use virtualisation software so you can install and run an older 32-bit version of Windows within Windows 7.
See Vmware Player http://www.vmware.com/products/player/
Or VirtualBox https://www.virtualbox.org/