Car will not start, has no spark

I have talked about my car problem with a few people, they thought it could have been the mobilizer, but it's not. Checked the coil packs, but it's not that.
There is no spark at spark plugs. Replaced main relay and tighten connectors, checked fuse #11(ignition coil) it's okay. Crankshaft position sensor replaced, car did start two days ago, battery charged, have gas, you can smell it, could it be the computer? I'm at my wits end. I need help, please, can you give me something or some ideas of where to check next. I have checked all kinds of areas of the car and can't seem to find out what is going on with this car of mine. It starts then it doesn't, then it starts and then it doesn't. It's like someone is playing a really bad joke on me but they aren't. Help!