I replaced HDD on Desktop but now say no boot device avail what to do Dell Inspiron desktop 660 2012

If you have replaced the entire HDD, it may not have an Operating System (boot device), so either you need to put the other HDD back in and put the OS onto a flash drive, from which you can plug in your new HDD and transfer the OS to your new hard drive. HOWEVER, it may be more efficient to buy a new OS in the form of a CD, and use it in your computer's DVD drive. (assuming your PC has one) These can be purchased at computer stores and office supply stores such as Best Buy and Staples.