It could be The load holding valve, it has a red **** on top. First of all, Did someone push on the **** and release it.....That`s all it takes. In an emergency lower of the tellies, you would depress the red ****, then screw in the prop valve adjuster until the mast lowered. If the **** is in the correct position, the load holding valve is stuck open. I would check the hydraulic filter for iron filings. TIP: to replace the filter without any oil coming out, raise the tellies up out of the free lift a few feet. There will be oil gushing out when you remove the filter. Most likely you will find iron filings in the system. they come from free lift cyl cushions falling apart. You must check for filings first, clean them out with magnet in hole, if you find any let me know, i`ll tell you what to do next. To test, Swap the load holding valve with another truck. Dont raise the tellies to replace the load holding valve!!!!!