Heat pump not powering on

Hi, would appreciate any help. A/C quit last night, went out to check today. Capacitor looks good. Noticed a small #3 blade fuse blown and replaced w/ no luck. Seen some other posts here about a contactor? Seems to be a possible reset button in middle on it (think I'm at right component) where the main power leads are attached. When I push in button, unit kicks on but back off when I release it. Is this possibly my problem? Thanks for any help