Car wont start please help ASAP/need to go to work

[1jimmy__d]

My car wont start ( this same thing happened last year!) I turn the key and I hear 1 click then go to crank it and nothing. Then I have no interior lights or any power at all. Yesterday this happened, I popped the hood. closed the doors and looked under neath the hood (basically did nothing). Went back inside and it started up fine. Come home and turn the car off. I went to start it up again, and nothing again. Sometimes I get interior lights with full power, but not enought to crank it over. other times very faint power, and others none at all. It can be jump started, however (temporary fix) the problem may pop up later on. I know the battery is still good and has water in the cells. The alternator is good too. Im guessing the starter is good seeing as how it cranks over fine with jumping it. Two years ago I replaced something under the driver side seat. Could this be the problem? the ignition? please help i need to go to work later today!! Thank you for any responses.

jim