Hi, I hope someone here can help me. I have a mid-2010 iMac. My hard drive failed and a tech person removed it for me. I bought a 32GB Cruzer Blade 323GB and installed a boot version of OSX High Sierra. I tested it on my MacBook Pro and it works. However, when I insert into my iMac I can't get it to work. The machine starts up and then I press the option key, but nothing. Just a black screen. After a short time I hear a fan noise. Inevitably I then have too manually shut down the iMac. Any ideas? Thanks in advance.