My tablet is stuck on "no command" screen. What can i do?
I had the same problem and I spent hours working on it.  

Excerpt from this article which helped fix my problem.

When flashing TWRP, do not reboot (into system) since the default "recovery.sh" file replaces TWRP on every boot. So I guess you need to flash TWRP again 

So next time you flash TWRP,
1) power off (preferably by pulling battery if nothing else works)
2) enter bootloader or fastboot mode by holding particular button combinations (Google your phone's model to find out)
3) boot into recovery (TWRP)  

NOTE that the first time you boot into recovery twrp will ask you wether you want to make changes to the system... Choose "yes"... And then you will have proper recovery (TWRP) working.