transmission linkage . clutch won't go into first

First you need to determine if it is a clutch, linkage, or trans problem. If it will not go into first with the engine running, but does go into first with the engine off, you may have a clutch release problem. Then you have to find out if it is cable release on the clutch, or hydraulic release. If it is hydraulic release, make sure the master cylinder for the clutch has fluid (most use brake fluid). If it was low on fluid, you must have a leak. If it will not go into first engine off or engine on, then linkage and trans are the next areas that would have to be looked at by a professional.