The latest Parallels update 10.1.2 (28859) released on or about 12-24-14 has a broken coherence mode. If you have the system entering coherence mode automatically, your system may appear to hang when starting Windows 7. You have to exit Coherence. My system is an early model 2014 MacbookPro with Windows 7 64 bit. I cannot run the latest Parallels version in Coherence at all and the Coherence option is greyed out. I also have a MacMini Server 2013 model that had a problem with Coherence but after two attempts did seem to enter Coherence fine.
Please follow the steps as suggested at: http://kb.parallels.com/111474 as you are unable to switch to Coherence mode. If the issue still persists, please create a Problem Report ID and send us the Problem Report ID number so that we will check it and assist you further. To create a Problem Report ID, please follow this link: http://kb.parallels.com/9058