Why won't a car that has been parked for years start?

Try turning the engine over with a wrench on the end of the crankshaft, removing the sparkplugs will make this easier, if you're unable to turn it, then it's seized. You will possibly need to do a full engine overhaul, to have any chance of starting it.

However, if you can turn it over this way, the fuel is likely to be 'Stale', the complete fuel system will need to be drained, cleaned (especially the fuel tank and carburettor), filters replaced and refilled with fresh fuel. Also check the ignition system, ensuring that there are sparks on all plugs (preferably new ones).