As part of routine maintenance, I changed the timing, alternator and power steering belts, water pump, oil seals for camshaft, crankshaft and oil pump, idler pulley and spring and the valve cover gasket. Car starts fine and timing is good but tachometer and odometer aren't working, can't put car into gear, alternator is not charging and my OBD II scan software is unable to connect. Any thoughts on what I did wrong?

PLEASE don't be offended when I ask you this, as you seem to know what you are doing, but did you disconnect the battery b4 disconnecting the alternator? Also, it would help to know what year and engine you have. Must be pretty new since it has obd2. New compared to mine anyway.
Steve

As part of routine maintenance, I changed the timing, alternator and power steering belts, water pump, oil seals for camshaft, crankshaft and oil pump, idler pulley and spring and the valve cover gasket. Car starts fine and timing is good but tachometer and odometer aren't working, can't put car into gear, alternator is not charging and my OBD II scan software is unable to connect. Any thoughts on what I did wrong?

Not an expert by any means... but check to see if the harness and connection from the alternator that passes next to the valve cover is not damages. When you removed the valve cover it may have gotten pulled or damaged the connection. Again.. no expert... Jenny