Hello, there is a PC on it now is Windows 7, I want to put a second Windows Server 2012 r2 with the prospect to carry then seven. Did zagruzochnogo a USB flash drive using Windows 7 USB DVD Download Tool when restart the computer - enter BIOS and boot menu run the flash drive, a black screen appears at the top left blinking underscore and silence, hanging. Tried other images, same result. What could be the problem?