Two things could cause this. (1) you don't have a bootable disk image in drive SY0: or (2) the emulator is waiting for you to press the SPACEBAR to autodetect the baud rate.
To insert a bootable disk
image in drive SY0 tap in the upper area of the screen to bring up the
disk library. Scroll down by swiping your finger until you see the disk
labeled "HDOS_3-02_1_System.h8d". Tap this disk image and it will be inserted in drive SY0.
Once you insert a bootable disk in SY0 tap the BOOT
button. If this is a distribution disk image that has never been booted
before the emulated system will wait for you to press the SPACEBAR so it can detect the baud rate. When you do this it should then boot to the operating system.
Note that once you use a disk it is copied to
your "My Images" section in the disk library. You can then select that
disk image from now on and you will not have to press the SPACEBAR
again.
