Mine did the same. Just continue to press the down arrow and hold it down until it gets to the very bottom. Continue to keep the down arrow down. Then it will reset by moving up a tiny bit. The display will say btm for bottom. Then you will be able to push the ip arrow and lift it back up. It happened because the power was disconnected. Hope this sort you out.
First, disconnect the appliance completely from the power supply. After reconnecting, the device should reset.
Reset procedure : Press keys 3 + 4 simultaneously for 5 seconds until RST is displayed. Hold down the down key to the lowest position. The message BOT appears. Then press the down button for 5 seconds until the table adjusts automatically. The table can then be used normally. Note: If the table rises slowly, it may be overloaded. Check the load capacity. Let the table rest for about 20 minutes, then try again.