Read it very carefully;
[HOW TO] Rooting Unlocking and De-Branding your ZTE Crescent [Updated Now Complete] - Android @ MoDaCo
If you decide to proceed then do it logically. Read and read some more of that post on page 1. If you decide to proceed then get the correct files together and use them in the order they are described. Check and double check you have all the files and the correct ones for your model before you start. Take your time and think about what you`re doing, ensure the phone is 100% charged before you start. Then you will have a better chance of success.
I unlocked my SFII and then rebooted it from the Restore menu (see link to post above for definition of Restore). In hindsight, I should have unlocked it, restarted to the Restore screen, wiped the data/factory, Cache and Dalvik Cache (Dalvik is on second page of Restore so use Advanced to get to it). Then applied the Crescent.zip as a flash from Restore, followed by the Sanfranciscokernel.zip (align the keyboard with that) then rebooted the system. Both zips are flashed by moving the up/down vol button to move through the menu then press HOME to select the apply zip from SD option Ten mins later I would have had an unlocked and debranded phone. But I hadn`t the confidence to take that last step and didn`t have those two files on my SD card. Now I have done it many times but because I simply restarted the phone I initially had great problems trying to get back to the Restore screen to apply the ROM change.