Question about jobs

I'm about to be done with school in May and graduate with a bachelors in Psychology (I know, useless). But regardless I wanted to look into enlisting and I just was having some trouble deciding some job options.

I'd like to join the FBI when I'm out, and I was thinking of a career in the Airforce as something I could use there, or if the career in the FBI didn't work. I'd love something either working with computers, or working on mechanics. Something where I wasn't just at a desk all day would be ideal. Any recommendations for a few jobs? Integrated avionics looked interesting. Any experience?