We need more details in order to recommend getting your engines running, if at all possible. First, as gjslsffan suggested, is your power pack working? Is there power getting to the track, or have you tried touching wires directly to the pickup wheels? What kind of engines do you have? Steam, diesel? You may need to disassemble them and clean hardened grease/lube from the gears. Are the motors open-frame? If so, have you cleaned the communtators (that's the part on the motor shaft that has a bunch of windings on the three to five poles? Are the wheels that pick up power from the track clean? It may take only swabbing them with some alcohol.
I'd suggest first getting the engines running on DC, and then you can consider whether to convert them to DCC. Installing decoders will require that the DC motors be isolated from the frame, which may or may not be a bit difficult. If you go to DCC, do you want sound? The difference between sound and silent converters is generally the price. With sound, it will be more expensive...usually running about $110 per decoder.
Let us know how we can help.