Have you tried jump-starting it? (if it doesn't start with a jump and does the same thing, don't keep trying)
If it starts with a jump, and then runs fine for a good while, but then wont start again unless you get another jump then you need a new battery.
If the jumpstart gets her going, but the motor dies or gets real sluggish as you turn on everything electrical (high beams, heat on high, etc) soon after you remove the jumper cables, your alternator is not charging the system.
If it does the same thing it has been doing when you try to jump it, then there is likely either a bad part (starter, solenoid,etc) or an electrical fault. This fault could be a grounded positive lead or a negative & positive wire are contacting each other somewhere.
The other electical fault possibility is a poor connection (technically a "high resistance open"). You checked the positive battery lead to the starter, but have you checked the battery ground? if it is making poor contact it will have the same effect. Make sure there's not a bunch of corrosion at the terminals or wherever it is bolted down.
I highly doubt that battery could have a decent charge after all you've been through. If you don't feel comfortable jump starting it, then I would buy/beg/borrow/steal a good one to at least try starting it.