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First, try pressing the fold switch (with the lift in the closed/retracted position.) Sometimes the hydraulics lose pressure over a period of disuse, and this re-pressurizes them.
Then, you could check for whether the inner roll stop barrier is in the locked position. If it is not, the lift won't operate. If it isn't locking into position, the lift won't work and it will need to be serviced.
Also, if the inner roll stop barrier is not locked and weight is sensed as on the platform, it will cut off power to the control pendant or hand control and the lift won't work.
Otherwise, unfortunately, your lift most likely either needs maintenance, or worse, needed it a while ago and did not receive it and will need repair-servicing.