car won't start after unused for 1 month

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i recently left the country for a month and when i came back the car would not start. first, there was no sound or activity when i turned the key; the battery was dead and the positive terminal was severely corroded. but after replacing the battery and terminal, the car still won't start. now when i turn the key it sounds like it will start, but never fully starts. instead, the engine revs unevenly. it is not a grinding but an uneven sound. it will sound like it might just be starting, but then it dies out if i let the key go. any suggestions for where to start? also, when i came back the alarm was set even though i did not set it, i thought that was strange.