6gen won't start after it has been sitting for a month Options

[gts4]

2.2l, 5sfe. Battery has yellow and blue corrosion or build up. Almost looks like dry foam. I used booster cables with a new car and tried a battery pack. I could get the interior lights on, but when I try cranking the engine I get nothing.

Ideas?

I've had the starter, alternator, and distributor all changed within the last year at different times. Could it be the fuel pump? I recently added my own gas with a canister right before I grounded it. Lastly, could I flood the engine by trying to turn it over too often when nothing happens? How can I diagnose this? Should I clean the battery terminals and try again? Should I change the battery altogether?

I'm thinking of keeping this in my collection instead of selling. So before I replace the fenders, doors, and hatch I'd like to make sure she's running perfectly. Thanks.