Late 2009 27" iMac won't boot after HDD replacement

Replaced my harddrive because the old one was failing (thousands of bad sectors). Replacement went smoothly, except that the Hitachi 1TB HDD I used as a replacement has no plug for the mac heat sensor cable. Assuming this would be okay aside from excessive fan spin, I just tied the cable out of the way. Now, the computer will not boot. If left alone it will quickly flash the questionmark folder before switching to the gray mac logo with infinitely spinning petals. If I try to hold any keys to boot from a disc, USB, or into verbose mode, the screen simply stays white indefinitely. So, is this simply a result of not having a drive wth a heat sensor port? Or is something else at work here, like potential moboard failure? I appreciate any help, thanks. :)