Dead Battery Charged, Engine Wont Start

Recently I left my headlights on all night, which drained my battery. I had a co-worker come over and attempt to use jumper cables - the engine woud turn over slowly, but the cables didn't provide enough "juice" to get it started. During the process, turning the ignition key was insucesso at gettin a response from the starter. After several attempts at trying to start it with jumper cables, I pulled the battery and took it into a shop and had it charged. The battery tested good after it was charged.

The next day I put the battery in, cleaned the posts and connectors vey well to ensure the electrons flow even better than before. When turning the key, I got all gauge indicators but didn't get any response from the starter. After checking fuses for possible damage and verifying that none were blown, I decided to replace the starter. Unforatunately I'm getting the same result - the starter doesn't do anything when I turn the key but everything else seems normal.

Can you lend any advice? My last though would be the starter relay - can I check that somehow? Thanks for any advice.