not sure how old this lift is but based on the newest manual this is the troubleshooting result for 'no lift'
4.2-4 Platform does not Lift
1. Open manual lowering valve V1.
- Close valve. Replace if defective.
2. Hydraulic oil level too low.
- Fully lower the platform. Fill hydraulic tank until fluid is at or slightly above the top mark on the
sight glass.
3. Platform weight excessive.
- Reduce platform load to maximum capacity.
4. Up valve 3H-14 or 3H-14A (Machines with end of stroke limit switch LS3 only) defective or is sticking.
- Check valve. Replace if defective.

knowing the serial number would have a bearing on the troubleshooting of components and selecting the correct service manual.
There are some limit switches on the scissor assembly at the base that could be causing a problem if they are damaged or not adjusted properly or some type of issue with the switch arm/wheels.