It sounds like the belt is not turning the alternator. The battery would go flat due to this, and also you may be expereincing your headlights going dim at night. eventualy the fuel pump may not be able to pump fuel, and the engine will stop.
Get it checked out, the garage will know the correct routing for the belt.
if you want to try fitting it again, make sure the alternator bracket is nice and adjusted, so the belt is very tight so when the engine runs, all the pulleys are rotating.
Then with a DC voltmeter and the engine running, rev the engine to 2000rpm, and measure across the battery, you should have about 13.8V to 14.2V to indicate tht the alternator is charging. Also the idiot light on the dash with the battery symbol should go out when the engine is running, to indicate the feild voltage is 12V.