Also make sure all the connections at the relay under the left side cover are clean and tight (connectors, screws...). Don't forget the chassis ground too.
I had weird problems, including everything suddenly quitting until I went through and tightened everything. Also, if you get sort of a grunting, buzzing noise when you hit the starter but the engine doesn't seem to turn over, that is a sign of a weak battery or otherwise low voltage to the starter; the relay/solenoid will make a weird, low buzz when there isn't enough juice to engage the starter and get things spinning. Put a volt meter on the battery. It should be reading a tiny bit more than 12v at rest and better than 13v when the engine is running and charging. I believe it shouldn't draw down much below 10v when you're cranking. If it really drops (8,7V), it's probably a bad battery.
How old is the battery? If it's original, it's certainly toast by now. If you do change it, do yourself a favor and wrap it in duct tape in such a way to make a lift handle - the battery is a pain to get out otherwise.