Why won't my stupid civic start?

I recently changed the thermostat, radiator hoses and water pump. I went out to lunch today and on my way back home my tachometer and temperature gauge where jumping around so I parked it. After i checked the fluids, which where nominal, she wouldn't crank. Lights and gauges still came on and the battery has a good charge.
Why won't my stupid civic start?
Sounds like a loose conection to me. Could be related to the alternator being that the alternator probably had to be removed to allow removal of the water pump. Could be a loose wire, loose ground cable or someone didn't place the protective rubber over the alternator's postive wire and it could have shorted against the frame. Chances are its one of the above or all. Hope you fix it soon.
Why won't my stupid civic start?
because it is a civic. Get a neon
Depending on the year of your vehicle,

If its an older model, it could be that the wires could be shorting out.

If its a newer model, it could be the computer witch is located up near the front of your engine,

If it is this, ouch!!!!! It can be very costly.
it would help if you state what year and engine size. every year ,honda change the electrical wire colors. to pin point your electrical problem, i need year and engine sizes
check the positive battery cable.although the cable may still be connected,there are several smaller wires that often partially or completly break off.i've seen it several times on olde hondas.
I really don't think that you have a problem with anything you just did. I had an 89 camaro that did that once it turned out to be the computer. Have it checked out at your local auto zone and if thats the problem make sure to check all the components of your ignition system because when a computer goes it tends to take the ignition system out with it.

GOOD LUCK!
IT MIGHT BE A temperature sensor