First check the fluid in the power trim unit.
If that is ok, check all of your electrical connections from the trim motor (disconnect connectors, clean and reconnect) to your engine...especially the ground. Check all grounds on your engine and make sure they are clean and free of corrosion.
Make sure you have a good strong battery.
Check for clean and tight connections at the battery.
Make sure that you have connected all the wires (for your accessories, etc) on your battery to the proper plus or minus terminal.
It could be just a trim motor ready to die, but could just be a connection that is not allowing current to flow.