Segui bene le istruzioni che trovi qui ONDA_V975m_V3_v1.1.0_rozak_20140414 - Onda Tablet Forum (validi anche per il firmware ufficiale) e che ti riporto di seguito:
Follow this steps exactly:
1- Extract the .rar file of the ROM. You will get these files:
aml_autoscript
factory_update_param.aml
recovery.img
u-boot.bin
update.zip
2- Put an SD card of size up to 16GB in card reader.
3- Format the SD card with SDFormatter version 4 (hint: run this program as administrator).
You can download it from here: SD Formatter 4.0 for SD/SDHC/SDXC - Tools for Onda v975m - Onda Tablet Forum
4- From the files you extracted in step 1 copy ONLY these files to SD card:
factory_update_param.aml
update.zip
5- Safely remove the SD card from the computer (Very important!).
6- Power off the tablet by pressing <Power> button for 20 seconds.
7- Put the SD card into the tablet's card slot.
8- Press simultaneously AND HOLD the buttons <Power> and <Volume +>.
9- When the green droid appears (or after about 5 seconds if no droid appears) release ONLY <Power> button. Keep pressing <Volume+>.
10- After about 1-3 minutes you will see the big droid with the spinning cube. Now release the <Volume+> button.
11- When the update finishes, the tablet will reboot. As soon as you see the ONDA logo, you are in business.